After Jesus was immersed [by John], He came up out of the water and heaven was opened up before Him and He saw the Holy Spirit from God descending, as a dove, and landing upon Him.

For what person knows the thoughts of a man except that man's [own] spirit which is in him? In the same way, no one knows the thoughts of God except God's Holy Spirit. But we [apostles] did not receive the spirit of the world [i.e., human wisdom. See verse 6], but the Holy Spirit from God, so that we could understand what was freely given to us from God [i.e., the gift of inspiration. See verses 9-10]. These also are the things we [apostles] speak, not in words taught by human wisdom, but [in words] taught by the Holy Spirit. We use [or, combine] Spirit-taught words to express [or, with] Spirit-given truth.read more.
Now the natural person [Note: Since this person is contrasted with the spiritual person of verse 15, it is taken here to mean the person without the Holy Spirit] does not receive the things [i.e., truths] revealed by the Holy Spirit of God, because they are [considered] foolishness to him. And he cannot understand them because they must be discerned by using spiritual judgment [i.e., judgment aided by the Holy Spirit].

You people show [i.e., by your conversions] that you are a letter from Christ, delivered by us [i.e., the result of our ministry], not written with ink but with the Holy Spirit of the living God; not on stone tablets [i.e., as in the case with Moses' ministry], but on tablets of the human heart. [See Jer. 31:33; Heb. 8:10].

For we [Christians] are the [true] circumcision [i.e., the real "Jews" in God's eyes. See Rom. 2:28-29]. We worship by means of God's Holy Spirit [i.e., are empowered and motivated by the Holy Spirit], and boast in [the person and work of] Christ Jesus, and [we] place no confidence in the flesh [i.e., in any outward ritual or status for salvation].

If you are spoken against for being Christians, you have God's blessing, because His glorious Holy Spirit rests upon you [to provide comfort, See John 14:16].