When we become possessed of this knowledge, that the Son of God is joined to us, we should cast our eyes upon that which is so highly set forth in Him; that is, the virtue and power of the Holy Ghost. So then, Jesus Christ did not only appear as man, but showed indeed that He was Almighty God as all the fulness of the Godhead dwelt in Him. If we once know this, we may well perceive that it is not without cause that St. Paul saith, all the treasures of wisdom are hidden in our Lord Jesus Christ.
When we have once laid hold on the promises of this Mediator, we shall know the height and depth, the length and breadth, yea, and whatsoever is necessary for our salvation: so that we may stay our faith upon Him, as upon the only true God; and likewise behold Him as our brother; who hath not only come near to us, but hath united and joined Himself to us in such a manner, that He hath become the same substance. If we have come to this, let us know that we have arrived to the perfection of wisdom, which is spoken of by St. Paul in another place; that we may fully rejoice in the goodness of God; for it bath pleased Him to lighten us with the brightness of His gospel, and to draw us into His heavenly kingdom.
This is from Calvin’s 27th sermon on 1 Timothy, probably preached the afternoon of December 16, 1554 in Geneva (according to T. H. L. Parker, Calvin’s Preaching, pp. 163-166) and may be found in the Banner of Truth fascimile of the 1579 edition of Calvin’s Sermons on Timothy and Titus (pp. 321-333). This sermon may be found online, from the Eerdman’s 1949 edition, here: The Mystery of Godliness (1 Timothy 3:16) – John Calvin.