The following is an excerpt from The MacArthur New Testament Commentary on 1 Corinthians 3.

A new building is usually checked out carefully before it is occupied or used.  Cities, counties, and states have codes that require buildings to meet certain standards. God has strict standards for what we build for Him in and with our lives. When Christ returns, every believer’s work will be tested as to quality. Fire is the symbol of testing. Just as it purifies metal, so will the fire of God’s discernment burn up the dross and leave what is pure and valuable (cf. Job 23:10; Zech. 13:9; 1 Pet. 1:17; Rev. 3:18).

That will not be a time of punishment but a time of reward. Even the one who has built with wood, hay, or straw will not be condemned; but his reward will correspond to the quality of his building materials. When wood, hay, or straw come in contact with fire they are burned up. Nothing is left but cinders. They cannot stand the test. Gold, silver, and precious stones, however, do not burn. They will stand the test, and they will bring great reward.

Believers who have right motives, proper conduct, and effective service build with gold, silver, and precious stones. They do constructive work for the Lord and will receive corresponding rewards. He shall receive a reward. That simple and hopeful promise is the message of eternal joy and glory. Whatever our service to God’s glory, He will reward.

Many humanly impressive and seemingly beautiful and worthwhile works that Christians do in the Lord’s name will not stand the test in “that day.” It “will become evident” (v. 13) that the materials used were wood, hay, and straw. The workmen will not lose their salvation, but they will lose a portion of any reward they might be expecting. They shall be saved, yet so as through fire. The thought here is of a person who runs through flames without being burned, but who has the smell of smoke on him—barely escaping! In the day of rewards, the useless and evil things will be burned away, but salvation will not be forfeited.

It is easy to fool ourselves into thinking that anything we do in the Lord’s name is in His service, just as long as we are sincere, hardworking, and well meaning. But what looks to us like gold may turn out to be straw, because we have not judged our materials by the standards of God’s Word—pure motives, holy conduct, and selfless service.