(Vs. 9.) This is a quotation from Isaiah 64:4 to prove that the gospel of Christ is mysterious and hidden wisdom, unknown to the wise and prudent of this world. This is not speaking of the happiness of heaven, but of the blessings and benefits of Christ, as the context shows. Though God's mercy to sinners in Christ is to be seen, read in Scripture and heard by preaching, the eye, ear and heart of natural man can neither see, hear, nor understand it (John 3:3; Matt. 13:13-16). The gospel must be revealed (1 John 5:20).
(Vs. 10.) Since the gospel is unknown to natural men (it is beyond the understanding of the wisest of them), how can any be acquainted with these spiritual mysteries? The answer is here in this verse. God has made a revelation of his purpose to save, of the person and work of Christ, and of how he can be just and Justifier by his Spirit (John 16:8-15). Our Quickener, Teacher and Comforter, the Holy Spirit, has a complete and perfect knowledge of everything that is, or belongs to, the gospel of Christ (Eph. 3:8-11).
(Vs. 11.) "What person knows and understands what passes through a man's thoughts except the man's own spirit within him?" A man's designs, purposes and intentions can never be known by another man unless the man's own spirit reveals them. Even so, the eternal purpose of God, the hidden wisdom of God and the mysteries of his love in Christ are known by no man. But the Spirit of God knows the thoughts of his heart, his purposes, will, ways and decrees.
(Vs. 12.) "We have not received the carnal spirit which belongs to this world (that is, the carnal wisdom, philosophy and thoughts of natural men, which lie in the wisdom of worldly things and follow them for worldly advantage); but we have been given by God, and have received, the Holy Spirit of God" (1 Cor. 1:19-21). He is the Spirit of truth, of illumination, of adoption and of comfort, and he is the seal and earnest of future glory. "God has given us his Spirit of truth that we may know, understand and appreciate the gifts of his divine favour and blessings so freely given to us by God in Christ Jesus" (Eph. 1:16-20; 1 John 1:1-4; Matt. 16:15-17).
(Vs. 13.) "And we are setting forth these truths in our preaching, not in words learned in the schools of philosophers or with the logic taught and understood by natural men, but we preach and teach the gospel in the language of the Scripture written by the Spirit of God. We interpret spiritual truth in spiritual language to spiritual people. The best interpreter of Scripture is Scripture (2 Peter 1:20, 21; 2 Tim. 3:16, 17). We compare the New Testament with the Old Testament, and their truth and harmony are seen (Luke 24:44-46; Acts 10:43).
(Vs. 14.) The natural, unregenerate man (whether in the world or in the church) will not receive, understand, nor believe in his heart these truths of God and the revelation of the Spirit of God. The gospel of grace, of a crucified Redeemer, is sheer nonsense to him. He is incapable of understanding these mysteries of God because they are understood in a spiritual manner, by spiritual light and by the revelation of the Holy Spirit. As there must be natural faculties to understand natural things, so there must be spiritual faculties to understand spiritual truth.
(Vs. 15.) "He that is spiritual includes every person who is born of the Spirit of God, breathes after spiritual things and has a saving interest in Christ. He discerns, not all things natural or all things spiritual (there are many things he does not know), but all things necessary to faith and salvation. These truths of sin, sovereignty, substitution and satisfaction in Christ are plain to him. The spiritual man himself is not understood by natural men. They do not know who he is, what he is, or why he believes as he does (John 15:17-21).
(Vs. 16.) "Who has known the deep counsels of God? Who knows the purpose of salvation in Christ? Who knows the hidden mysteries in the types and shadows of the Old Testament that he may instruct this spiritual man? It is certainly not the philosophers or the wise men of this world. But we apostles are abundantly qualified to instruct him, for we have the mind of Christ" (Eph. 4:11-15).