New believers were entering the new covenant inaugurated by Jesus blood from the day of Pentecost onward.
There is no other way to be saved--
Act 2:38 Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost.
Act 2:39 For the promise is unto you, and to your children, and to all that are afar off, even as many as the Lord our God shall call.
Act 2:40 And with many other words did he testify and exhort, saying, Save yourselves from this untoward generation.
Act 2:41 Then they that gladly received his word were baptized: and the same day there were added unto them about three thousand souls.
Act 2:42 And they continued stedfastly in the apostles' doctrine and fellowship, and in breaking of bread, and in prayers.
Act 2:43 And fear came upon every soul: and many wonders and signs were done by the apostles.
Act 2:44 And all that believed were together, and had all things common;
Act 2:45 And sold their possessions and goods, and parted them to all men, as every man had need.
Act 2:46 And they, continuing daily with one accord in the temple, and breaking bread from house to house, did eat their meat with gladness and singleness of heart,
Act 2:47 Praising God, and having favour with all the people. And the Lord added to the church daily such as should be saved.
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