4:1 Everyone should count Paul and other Christian workers as "servants" of Christ, fully responsible to him and not to the Corinthians. The phrase "those entrusted with" means "house stewards" and refers to a position often held by a slave (e.g., Joseph, Ge. 39:2-19) entrusted with managing the affairs of a household. "The secret things of God" indicates the mysteries of salvation God has revealed in his Word (Rom. 16:25; Eph. 9; 3:3-4; 1 Tim. 3:16)- things one cannot discover by human wisdom (cf. 2:1). These truths of the cross have been entrusted to Christian workers to be carefully used and guarded. As subordinate servants of Christ, they have no right of authority over those truths, but must minister them in Christ's name to God's people.
4:2-4 Paul now examines the character of those who are handling God's truth: they, including himself, must first of all show themselves faithful. Since he is the Lord's servant and steward, it is to the Lord that he owes responsibility, and it is the Lord who "judges" him for the quality of his service. Human judgment has little value; even self-evaluation is unreliable. Christ is Lord of the conscience and the one who can evaluate it properly.
4:5 The apostle leaps forward to the return of Christ when all Christians will have their works examined at the judgment seat of Christ (2 Cor. 5:10). Because of this, he charges the Corinthians not to judge his faithfulness, for this can be done truthfully only by the Lord when he returns. Therefore, knowing that the Corinthians are already judging him and others, he says to them in effect, "Curb your habit of judging."
"What is hidden in darkness" are the acts and motives concealed in the inner recesses of a person's mind and heart. Paul says the Lord will "expose the motives of men's hearts" as an explanation of his statement, "He will bring to light what is hidden in darkness." Thus, at the second coming of Christ, those who have been faithful in their work for the Lord will receive praise from him (cf. 3:8; also the parables in Matt. 25:14-23; Lk. 19:12-19). As the final judging must be done by God, so one's final praise will come from him.
[NIV BIBLE COMMENTARY Volume 2: New Testament].
JESUS IS LORD.