Nope. Still in Acts 2 verses 36-38
Therefore let the whole house of Israel know for certain that God has made him both Lord and Messiah, this Jesus whom you crucified."
37
Now when they heard this, they were cut to the heart, and they asked Peter and the other apostles, “What are we to do, my brothers?”
38
Peter (said) to them,
"Repent and be baptized, 7 every one of you, in the name of Jesus Christ for the forgiveness of your sins; and you will receive the gift of the holy Spirit.
Therefore membership into this body is not just MERE believing. How they became part of this body is by baptism.
That is why in 1 Peter 3: 18-22
For Christ also suffered for sins once, the righteous for the sake of the unrighteous, that he might lead you to God. Put to death in the flesh, he was brought to life in the spirit.
19
In it he also went to preach to the spirits in prison,
20
who had once been disobedient while God patiently waited in the days of Noah during the building of the ark, in which a few persons, eight in all, were saved through water.
21
This prefigured baptism, which saves you now. It is not a removal of dirt from the body but an appeal to God
7 for a clear conscience, through the resurrection of Jesus Christ,
22
who has gone into heaven and is at the right hand of God, with angels, authorities, and powers subject to him.
Yes, indeed the Lord is adding to those believers, but these group are not MERE believers, these group originated with the 12 at Pentecost and grew. And how they were added was through baptism. Those who believed were then baptised.
And I already have. That is why I said the Church is indeed the Body of Christ. And you rightly pointed out Ephesians. And what you completely missed in reading Ephesians is that Paul was already talking about the living and growing Body of Christ. But to become a member of this Church, more is required than just MERE belief. That is what I was trying to point out which you missed.
So yes, as verse 16 goes “
from whom the whole body, being fitted and held together by what every joint supplies, according to the proper working of each individual part, causes the growth of the body for the building up of itself in love.”
Each of us has a part to play as part of the entire Body.
BUT FIRST, WE MUST BECOME A PART OF THAT BODY AND HOW THAT HAPPENS IS THROUGH BAPTISM.