We must now examine this question. How do we receive those benefits which the Father bestowed on his only-begotten Son—not for Christ’s own private use, but that he might enrich poor and needy men? First, we must understand that as long as Christ remains outside of us, and we are separated from him, all that he has suffered and done for the salvation of the human race remains useless and of no value for us. Therefore, to share with us what he has received from the Father, he had to become ours and to dwell within us. For this reason, he is called “our Head” [Eph. 4:15], and “the first-born among many brethren” [Rom. 8:29]. We also, in turn, are said to be “engrafted into him” [Rom. 11:17], and to “put on Christ” [Gal. 3:27]; for, as I have said, all that he possesses is nothing to us until we grow into one body with him. It is true that we obtain this by faith. Yet since we see that not all indiscriminately embrace that communion with Christ which is offered through the gospel, reason itself teaches us to climb higher and to examine into the secret energy of the Spirit, by which we come to enjoy Christ and all his benefits… the Holy Spirit is the bond by which Christ effectually unites us to himself.
Institutes of the Christian Religion, Volumes 1 & 2, ed. John T. McNeill, trans. Ford Lewis Battles, The Library of Christian Classics (Louisville, KY: Westminster John Knox Press, 2011) Vol. 1, p. 537. Book 3.1.1