What does “the fullness of him who fills all in all” (Eph. 1:23) mean?

Let’s look at the entire sentence, which is found in verses 22-23:  “And he put all things under his feet and gave him as head over all things to the church, which is his body, the fullness of him who fills all in all.”

Basically, Paul is saying that God the Father put all things under His Son’s feet and gave Jesus as head over all things to the church.  He then describes the church as Christ’s body before also depicting it as “the fullness of him who fills all in all.”

Paul later described Jesus to the Ephesians as “fill(ing) all things” (Eph. 4:10).  He told the Colossians that “Christ is all, and in all” (Col. 3:11).  More specifically, he wrote to them:

“For by him all things were created, in heaven and on earth, visible and invisible, whether thrones or dominions or rulers or authorities — all things were created through him and for him.  And he is before all things, and in him all things hold together.”  (Col. 1:16-17)

This omnipresence of Christ is fitting, considering that He is Deity (John 1:1-5, 14).  Jesus indeed “fills all in all” (Eph. 1:23).

The question now is this.  What fills up the One who “fills all in all”?

A careful examination of Ephesians 1:22-23 shows that the answer is “the church, which is his body.”  The body of Christ, which is specifically cited as being the church, is “the fullness of him who fills all in all.”

Christ fills up everything (“fills all in all”), and His body, the church, fills Him up (“the fullness of him”).

This gives insight into what it means to be “baptized INTO Christ” (Rom. 6:3; Gal. 3:27 – emphasis mine) and “baptized INTO one body” (1 Cor. 12:13 – emphasis mine).  That “one body” (compare with Ephesians 4:4-6) is the same “body” discussed in Ephesians 1:22-23, the “body” which is specifically said to be “the church.”  The body which is His church is what fills up Christ.  Thus, when one is “baptized INTO Christ” (Rom. 6:3; Gal. 3:27 – emphasis mine), one is baptized into what fills Him up…His body, which is His church.  To be baptized into Christ and be baptized into one body means the same thing.

When one is baptized into the body of Christ which is His church (of which there is only one since the New Testament specifically says there is “one body” – Eph. 4:4; 1 Cor. 12:13), then one is baptized into Christ.