And so it would seem that we are in agreement that Baptists (and some others) are incorrect when they say that the body of Christ was formed or born on the Day of Pentecost.
The church, the body of Christ is made up of believers. We know that at least 120 were believers as at least that many saw Jesus ascend into heaven, had accepted Him as messiah, Lord and risen savior days before the Day of Pentecost.
Thus even before the assembled believers spake with tongues on the Day of Pentecost, and even before the 3000 were saved, the body of Christ was already formed, already born and already in existence.
Thus, what occured to the Apstles, disciples and those assembled together in Acts 2:4 (at least 120) was a subsequent, distinct act to their salvation.
They were not baptized into the body of Christ on the day of Pentecost. The Body of Christ wasn’t formed or born on the Day of Pentecost. They were already baptized into the body of Christ, were believers, were saved, and formed the body of Christ BEFORE Acts 2:4.
What was distinctive here at Pentecost was the baptism with holy spirit as promised earlier. Thus that body of 120 souls became a spirit begotten body, the body of Christ according to 1 Cor. 12:12-27.
You must preface that remark ... the church, the body of Christ is made up of New Testament believers ... why?
Because THE distinguishing mark of a believer in Jesus Christ, verses an OT believer, is the permanent indwelling of the Holy Spirit.
It is the sealing of the Spirit ... the permanent indwelling in the Christians life. The OT saints did not have the permanent indwelling of the Spirit. When did that permanent indwelling begin? Pentecost. Therefore ... the church began at Pentecost because the permanent indwelling began at Pentecost.