1 Corinthians 2:16

For who hath known the mind of the Lord
The deep counsels of his heart, the scheme of salvation by Jesus Christ, as drawn in his eternal mind, the sense of the Spirit of God in the writings of the Old Testament, the things of the Spirit of God, or the doctrines of grace more clearly revealed under the Gospel dispensation; not any natural man, by the light of truth and strength of reason, has known any of these things. The apostle either cites or alludes to ( Isaiah 40:13 )

that he may instruct him?
not the Lord, who needs no instruction from any, nor can any teach and instruct him, nor would any be so bold and insolent as to attempt it nor does the knowledge of the mind of the Lord qualify any for such a work; since if he knows ever so much of it, he cannot know more than the Lord himself: but the spiritual man, whom a natural man, being ignorant of the mind of the Lord, cannot instruct; and so the words give a very proper and sufficient reason why the spiritual man is not discerned, judged, convinced, and instructed by the natural man:

but we have the mind of Christ;
the same with "the mind of the Lord" which proves that Christ is the Lord, or Jehovah, and so truly and properly God; and which is to be understood, not only of the apostles and ministers of the Gospel, but of all true believers; and therefore want no instruction, as they can have none from the natural man; though chiefly of the former, whereby they were abundantly qualified for the further instruction even of spiritual men.