1 Corinthians 12:12

The apostle here makes out the truth of what was above asserted, and puts the gifted men among the Corinthians in mind of their duty, by comparing the church of Christ to a human body. I. By telling us that one body may have many members, and that the many members of the same body make but one body (Co1 12:12): As the body is one, and hath many members, and all members of that one body, being many, are one body, so also is Christ; that is, Christ mystical, as divines commonly speak. Christ and his church making one body, as head and members, this body is made up of many parts or members, yet but one body; for all the members are baptized into the same body, and made to drink of the same Spirit, Co1 12:13. Jews and Gentiles, bond and free, are upon a level in this: all are baptized into the same body, and made partakers of the same Spirit. Christians become members of this body by baptism: they are baptized into one body. The outward rite is of divine institution, significant of the new birth, called therefore the washing of regeneration, Tit 3:5. But it is by the Spirit, by the renewing of the Holy Ghost, that we are made members of Christ's body. It is the Spirit's operation, signified by the outward administration, that makes us members.

— Matthew Henry's Concise Commentary (public domain)

Unity, not unvarying uniformity, is the law of God in the world of grace, as in that of nature. As the many members of the body compose an organic whole and none can be dispensed with as needless, so those variously gifted by the Spirit, compose a spiritual organic whole, the body of Christ, into which all are baptized by the one Spirit. of that one body--Most of the oldest manuscripts omit "one." so also is Christ--that is, the whole Christ, the head and body. So Psa 18:50, "His anointed (Messiah or Christ), David (the antitypical David) and His seed."

— Jamieson-Fausset-Brown Commentary (public domain)