In context the "But" which begins verse 14 shows a change in transition. The verses previous to verse 14 are indeed referring to "us" and "we" who have received. Verse 14 is not referring to the "us" and "we" of the previous verses, but rather in reference to those who don't receive and who cannot understand.
Let's look at the text brother:
But as it is written: What no eye has seen and no ear has heard, and what has never come into a man's heart, is what God has prepared for those who love Him. Now God has revealed them to us by the Spirit, for the Spirit searches everything, even the deep things of God. For who among men knows the concerns of a man except the spirit of the man that is in him? In the same way, no one knows the concerns of God except the Spirit of God. Now we have not received the spirit of the world, but the Spirit who is from God, in order to know what has been freely given to us by God. We also speak these things, not in words taught by human wisdom, but in those taught by the Spirit, explaining spiritual things to
spiritual people. But the
natural man does not welcome what comes from God's Spirit, because it is foolishness to him; he is not able to know it since it is evaluated spiritually. The
spiritual person, however, can evaluate everything, yet he himself cannot be evaluated by anyone. 16 For: who has known the Lord's mind, that he may instruct Him? But we have the mind of Christ.
Brothers, I was not able to speak to you as spiritual people but as
people of the flesh, as babies in Christ. I fed you milk, not solid food, because
you were not yet able to receive it. In fact,
you are still not able, because you are still fleshly. For since there is envy and strife among you, are you not
fleshly and living like ordinary people?
Read through this text again and notice the distinction Paul makes between the
natural/flesh people and the
spiritual people.
Here is what we can conclude:
1. The Natural man cannot receive these things Paul is addressing
2. The Spiritual man can receive these things Paul is addressing
3. The BRETHREN (believers) are not being "spiritual" and cannot receive these things Paul is addressing
Thus, the "things" Paul is addressing here cannot be in reference to the simple gospel truth (milk) because the "brethren" (believers) cannot receive them.