A follow up note:
Acts 2:38 is common restatement of the historical Jewish cultural and religious practices, with the addition of the receiving of the Holy Ghost, as promised in scripture.
One of the obvious doctrines what we so often over look is this one: The Apostles' doctrine is nothing more nor anything less than the sum total doctrines that Jesus Christ taught. Therefore, if one does not know, understand and practice the doctrines (including the commandments) of Christ, that person is not a follower of the Apostles' doctrines, much less a true disciple of Christ. That too is Bible (
Matthew 28:20, in context)