Charles Spurgeon Commentary Acts 9:26

"And when he was come to Jerusalem, he assayed to join himself to the disciples: and they were all afraid of him, not believing that he was a disciple." — Acts 9:26 (ASV)

They did not admit anybody and everybody into the Church.

They guarded it as Christ's Church should be guarded, so that unworthy people might not enter it. If any of you should be kept back a little while, you can say to yourself, "Well, they kept back Paul." We are poor fallible creatures, but we try to judge rightly concerning those who wish to unite with us.