John Gill Commentary 1 Chronicles 9:21

"Zechariah the son of Meshelemiah was porter of the door of the tent of meeting." — 1 Chronicles 9:21 (ASV)

And Zechariah the son of Meshelemiah
Some think this refers to one that was in the times of David; but it seems rather to respect one that was after the Babylonish captivity, see (1 Chronicles 26:1 1 Chronicles 26:2) though he and his brethren were in an office established in the times of David, and the order of which was now, as then, observed:

was porter of the door of the tabernacle of the congregation :
who was the chief porter, and kept the door; either that led into the outer court, and kept out all unclean persons from entering there; or that which led into the court of the priests, that none but priests might enter there.