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Brothers and sisters, when I came to you I didn't try to impress you with wonderful words or great wisdom when I told you what God had to say to you. I decided that while I was with you I didn't want to concentrate on anything except Jesus Christ, and that he was crucified. I came to you in weakness, fearful and trembling. I didn't speak to you with persuasive words of wisdom to convince you. I just explained it all to you through the evidence and power of the Spirit. That way your trust in God wouldn't rely on human wisdom but on the power of God.
However, we do use words of wisdom when we speak to those who are spiritually mature, but this isn't wisdom that comes from this world, or from the rulers of this world who soon fade from the scene. On the contrary we explain God's wisdom in terms of a revealed mystery*When the word mystery is used in the New Testament it is normally referring to a revealed mystery—particularly in reference to God becoming human in the person of Jesus Christ. that was previously hidden which God planned for our glory before the creation of the worlds.
None of the rulers of this world understood anything about this—for if they had, they would not have crucified the Lord of glory. But as Scripture says, “No one has ever seen, and no one has ever heard, and no one has ever imagined what God has prepared for those who love him.”From Isaiah 64 and Isaiah 65. 10 But God has revealed this to us through the Spirit, because the Spirit delves into the depths of God. 11 Who knows anyone's thoughts except the actual person?Literally, “who among men knows the things of a man except the spirit of the man that is in him?” In the same way no one knows God's thoughts except the Spirit of God. 12 For we have received the Spirit from God, not the spirit of this world, so that we could understand what God so generously gave us. 13 That's what we speak about—not using words taught by human wisdom, but what the Spirit teaches. We explain what is spiritual using spiritual terms. 14 Of course people who are not spiritual don't accept what comes from God's Spirit. It's just foolish nonsense to them, and they can't understand it, because what is spiritual has to be properly examined. 15 People who are spiritual investigate everything, but are not placed under investigation themselves.§“Investigate/investigation”—the same word is used in the original, and can also mean to examine or to judge. It is also related to the word translated “examined” in verse 14. English does not capture the subtlety of the original. 16 For “who understands the Lord's mind, and would think to instruct him?”*Quoting Isaiah 40:13. But we do have Christ's mind!
 

*2:7 When the word mystery is used in the New Testament it is normally referring to a revealed mystery—particularly in reference to God becoming human in the person of Jesus Christ.

2:9 From Isaiah 64 and Isaiah 65.

2:11 Literally, “who among men knows the things of a man except the spirit of the man that is in him?”

§2:15 “Investigate/investigation”—the same word is used in the original, and can also mean to examine or to judge. It is also related to the word translated “examined” in verse 14. English does not capture the subtlety of the original.

*2:16 Quoting Isaiah 40:13.