Many commentators understand John’s baptism of Jesus to be in view.1 However, given the fact that Jesus only called his disciples after he was already baptized (see Mark 1:9–20), this criteria would actually exclude many of those who were already apostles. More likely John’s baptism refers to the ministry of John which focused on preparing the Jewish nation for the coming of the Messiah.2 The baptism of John refers to John’s baptizing ministry, also seen in Acts 10:37.3
22 beginning from the baptism of John until the day when he was taken up from us one of these men must become with us a witness to his resurrection.”