The following is an excerpt from The MacArthur New Testament Commentary on Philippians 2.

work out your salvation with fear and trembling; (2:12e)The fifth motive for believers’ working out their sanctification is understanding the consequences of sin. Although God is loving, merciful, and forgiving, He nevertheless holds believers accountable for disobedience. Like John, Paul understood well that “if we say that we have no sin, we are deceiving ourselves and the truth is not in us. If we confess our sins, He is faithful and righteous to forgive us our sins and to cleanse us from all unrighteousness” (1 John 1:8–9). Knowing that he serves a holy and just God, the faithful believer will always live with fear and trembling. Fear translates phobos, which describes fright or terror (cf. Matt. 14:26; Luke 21:26; 1 Cor. 2:3) as well as reverential awe (cf. Acts 2:43; 9:31; 2 Cor. 5:11; 7:1). Trembling is from tromos, which refers to shaking and is the word from which the English word tremor derives. Both of those are proper reactions to the awareness of one’s own spiritual weakness and the power of temptation. The Lord seeks such an attitude in His children, as His words in Isaiah 66:2 indicate: “To this one I will look, to him who is humble and contrite of spirit, and who trembles at My word.”

An important Old Testament truth is “The fear of the Lord is the beginning of wisdom” (Ps. 111:10; cf. Prov. 1:7; 9:10). This is not a fear of being doomed to eternal torment, nor a hopeless dread of judgment that leads to despair. It is rather a reverential fear, a holy concern to give God the honor He deserves and avoid the chastening of His displeasure. Such fear protects against temptation and sin and gives motivation for obedient, righteous living.

Aware of his own personal weakness, Paul spoke of his “fear and … trembling” as he ministered to the church in Corinth (1 Cor. 2:3), and later of those believers who received Titus with the same kind of “fear and trembling” (2 Cor. 7:15). This kind of “fear and trembling” is closely related both to obedience to the Lord and to love and affection for Him and for fellow believers. It is for that reason that Solomon could declare: “How blessed [happy] is the man who fears always” (Prov. 28:14).

Such fear involves self-distrust, a sensitive conscience, and being on guard against temptation. It necessitates opposing pride, and being constantly aware of the deceitfulness of one’s heart, as well as of the subtlety and strength of one’s inner corruption. It is a dread that seeks to avoid anything that would offend and dishonor God.

Believers should have a serious dread of sin and yearning for what is right before God (cf. Rom. 7:14ff.). Aware of their weakness and the power of temptation, they should fear falling into sin and thereby grieving the Lord. Godly fear protects them from wrongfully influencing fellow believers, compromising their ministry and testimony to the unbelieving world, enduring the Lord’s chastening, and from sacrificing joy.

To have such godly fear and trembling involves more than merely acknowledging one’s sinfulness and spiritual weakness. It is the solemn, reverential fear that springs from deep adoration and love. It acknowledges that every sin is an offense against holy God and produces a sincere desire not to offend and grieve Him, but to obey, honor, please, and glorify Him in all things. Those who fear the Lord willingly accept the Lord’s chastening, knowing that God “disciplines us for our good, so that we may share His holiness” (Heb. 12:10). This fear and trembling will cause believers to pray earnestly for God’s help in avoiding sin, as the Lord taught them: “Do not lead us into temptation, but deliver [rescue] us from evil” (Matt. 6:13). That prayer again reflects the spiritual tension that exists between believers’ duty and God’s power.

Work out translates a present middle imperative of katergazomai and indicates a command that has a continuing emphasis. The idea is, “Keep on working out to completion, to ultimate fulfillment.” Heauton, here rendered your, actually has the more emphatic meaning of “your own.” The command is for believers to make a continuing, sustained effort to work out to ultimate completion their salvation, which has been graciously granted to them by God through their faith in Jesus Christ.

The principle of working out salvation has two aspects. The first pertains to personal conduct, to faithful, obedient daily living. Such obedience obviously involves active commitment and personal effort, for which Scripture is replete with injunctions, both negative and positive. Sin in every form is to be renounced and put off and replaced by righteous thinking. Believers are to cleanse themselves “from all defilement of flesh and spirit, perfecting holiness in the fear of God” (2 Cor. 7:1), setting their minds “on the things above, not on the things that are on earth,” because they have died to sin and their lives are now “hidden with Christ in God” (Col. 3:2–3). Just as they once “presented [their] members as slaves to impurity and to lawlessness, resulting in further lawlessness,” they should “now present [their] members as slaves to righteousness, resulting in sanctification” (Rom. 6:19), walking “in a manner worthy of the calling with which [they] have been called” (Eph. 4:1).

The apostle exhorted the Corinthians to strenuous effort in living the Christian life:  Do you not know that those who run in a race all run, but only one receives the prize? Run in such a way that you may win. Everyone who competes in the games exercises self-control in all things. They then do it to receive a perishable wreath, but we an imperishable. Therefore I run in such a way, as not without aim; I box in such a way, as not beating the air; but I discipline my body and make it my slave, so that, after I have preached to others, I myself will not be disqualified. (1 Cor. 9:24–27)His words later in the present letter also demand aggressive Christian living:  Not that I have already obtained it or have already become perfect, but I press on so that I may lay hold of that for which also I was laid hold of by Christ Jesus. Brethren, I do not regard myself as having laid hold of it yet; but one thing I do: forgetting what lies behind and reaching forward to what lies ahead, I press on toward the goal for the prize of the upward call of God in Christ Jesus. Let us therefore, as many as are perfect, have this attitude; and if in anything you have a different attitude, God will reveal that also to you; however, let us keep living by that same standard to which we have attained. (Phil. 3:12–16)He exhorted Timothy: “Flee from these [evil] things, you man of God, and pursue righteousness, godliness, faith, love, perseverance and gentleness. Fight the good fight of faith; take hold of the eternal life to which you were called, and you made the good confession in the presence of many witnesses” (1 Tim. 6:11–12; cf. 4:15–16; Heb. 12:1–3). To the Colossians Paul wrote:  So, those who have been chosen of God, holy and beloved, put on a heart of compassion, kindness, humility, gentleness and patience; bearing with one another, and forgiving each other, whoever has a complaint against anyone; just as the Lord forgave you, so also should you. And beyond all these things put on love, which is the perfect bond of unity. Let the peace of Christ rule in your hearts, to which indeed you were called in one body; and be thankful. Let the word of Christ richly dwell within you, with all wisdom teaching and admonishing one another with psalms and hymns and spiritual songs, singing with thankfulness in your hearts to God. Whatever you do in word or deed, do all in the name of the Lord Jesus, giving thanks through Him to God the Father. (Col. 3:12–17; cf. vv. 5–11)If living the Christian life were merely a matter of passive yielding and surrender, of “letting go and letting God,” then such admonitions not only would be superfluous but presumptuous. But those injunctions, and countless others like them throughout God’s Word, presuppose believers’ personal responsibility for obedience. They must choose to live righteously, to work out their salvation in daily living, while at the same time realizing that all the power for that obedience comes from God’s Spirit.

The second aspect of working out one’s salvation is perseverance, of faithful obedience to the end. Salvation has three time dimensions: past, present, and future. The past dimension is that of justification, when believers placed their faith in Jesus Christ as Savior and Lord and were redeemed. The present dimension is sanctification, the time between a believer’s justification and his death or the Rapture. The future aspect is glorification, when salvation is completed and believers receive their glorified bodies. Believers therefore have been saved, are being saved, and will be saved. They are to pursue sanctification in this life to the time of glorification. In that glorious moment believers will see the Lord “face to face” and come to know fully even as they are fully known (1 Cor. 13:12). They “will be like Him, because [they] will see Him just as He is” (1 John 3:2). It was for that glorious moment that Paul so deeply longed. Looking forward to that time he exclaimed:  More than that, I count all things to be loss in view of the surpassing value of knowing Christ Jesus my Lord, for whom I have suffered the loss of all things, and count them but rubbish so that I may gain Christ, and may be found in Him, not having a righteousness of my own derived from the Law, but that which is through faith in Christ, the righteousness which comes from God on the basis of faith, that I may know Him and the power of His resurrection and the fellowship of His sufferings, being conformed to His death; in order that I may attain to the resurrection from the dead. Not that I have already obtained it or have already become perfect, but I press on so that I may lay hold of that for which also I was laid hold of by Christ Jesus. Brethren, I do not regard myself as having laid hold of it yet; but one thing I do: forgetting what lies behind and reaching forward to what lies ahead, I press on toward the goal for the prize of the upward call of God in Christ Jesus. (Phil. 3:8–14)Because the fulfillment of that hope was a divinely decreed certainty, Paul could say with complete confidence that “salvation is nearer to us than when we believed” (Rom. 13:11). Although it is not yet completed, the testimony of Scripture is that every believer’s salvation is utterly secure.

In the Olivet Discourse, Jesus declared, “The one who endures to the end, he will be saved” (Matt. 24:13). Paul and Barnabas urged new believers in Pisidian Antioch “to continue in the grace of God” (Acts 13:43) and encouraged “them to continue in the faith” (14:22). In his letter to the church at Rome, Paul declared that God will give eternal life “to those who by perseverance in doing good seek for glory and honor and immortality” (Rom. 2:7; cf. 11:22). He promised the Colossians that Christ would present them before God the Father “blameless and beyond reproach—if indeed [they] continue in the faith firmly established and steadfast, and not moved away from the hope of the gospel that [they] have heard” (Col. 1:22–23). He admonished Timothy: “Pay close attention to yourself and to your teaching; persevere in these things, for as you do this you will ensure salvation both for yourself and for those who hear you” (1 Tim. 4:16). The writer of Hebrews notes, “We have become partakers of Christ, if we hold fast the beginning of our assurance firm until the end” (Heb. 3:14; cf. 8:9; 10:38–39; cf. James 1:22–25). In each of His letters to the seven churches in Asia, the Lord described believers as overcomers (Rev. 2:7, 11, 17, 26; 3:5, 12, 21).

Perseverance in the faith is the duty of every true believer, and yet not the power of their security. It is, however, the unmistakable and inevitable evidence of divine power operating in the soul (Col. 1:29).

Believers will persevere because God’s power keeps their salvation secure. Jesus repeatedly emphasized that truth. To the multitudes at Capernaum, He declared emphatically that “all that the Father gives Me will come to Me, and the one who comes to Me I will certainly not cast out. This is the will of Him who sent Me, that of all that He has given Me I lose nothing, but raise it up on the last day” (John 6:37, 39). Later, in Jerusalem, He declared, “I give eternal life to them, and they will never perish; and no one will snatch them out of My hand. My Father, who has given them to Me, is greater than all; and no one is able to snatch them out of the Father’s hand” (John 10:28–29; cf. 17:2, 12, 24; 18:9). Earlier in Philippians, Paul wrote that he was “confident of this very thing, that He who began a good work in you will perfect it until the day of Christ Jesus” (1:6). Peter gave believers a similar assurance, saying that they “are protected by the power of God through faith for a salvation ready to be revealed in the last time” (1 Peter 1:5).

From beginning to end, the entire divine work of salvation is under God’s control. In a well-loved passage Paul wrote,  We know that God causes all things to work together for good to those who love God, to those who are called according to His purpose. For those whom He foreknew, He also predestined to become conformed to the image of His Son, so that He would be the firstborn among many brethren; and these whom He predestined, He also called; and these whom He called, He also justified; and these whom He justified, He also glorified. (Rom. 8:28–30)To the Ephesians he wrote, “For by grace you have been saved through faith; and that not of yourselves, it is the gift of God; not as a result of works, so that no one may boast. For we are His workmanship, created in Christ Jesus for good works, which God prepared beforehand so that we would walk in them” (Eph. 2:8–10).

So the call for believers to work out their salvation is found all through the New Testament. That is only fitting and proper, since it is a call for the necessary commitment on the believer’s part that is a prerequisite for the joys, blessings, and usefulness of sanctification.