“By those dimensions Paul means nothing else than the love of Christ, of which he speaks afterwards. The meaning is, that he who knows it fully and perfectly is in every respect a wise man.
As if he had said, “In whatever direction men may look, they will find nothing in the doctrine of salvation that does not bear some relation to this subject.”
The love of Christ contains within itself the whole of wisdom.
Almost all men are infected with the disease of desiring useless knowledge.
Therefore this admonition is very useful: what is necessary for us to know, and what the Lord desires us to contemplate, above and below, on the right hand and on the left, before and behind.
The love of Christ is held out to us as the subject which ought to occupy our daily and nightly meditations, and that which we ought to be wholly immersed in. (Ephesians 3:18-19)
He who holds to this alone has enough.
Beyond it there is nothing solid, nothing useful, nothing, in short, that is right or sound.
Go abroad in heaven and earth and sea, you will never go beyond this without overstepping the lawful bounds of wisdom.”
–John Calvin, Calvin’s New Testament Commentaries: Galatians, Ephesians, Philippians, and Colossians, Volume 11, Trans. T.H.L. Parker (Grand Rapids, MI: Eerdmans, 1965), 168-169. Calvin is commenting on Ephesians 3:18-19.