John Gill Commentary Mark 14:13

"And he sendeth two of his disciples, and saith unto them, Go into the city, and there shall meet you a man bearing a pitcher of water: follow him;" — Mark 14:13 (ASV)

And he sends forth two of his disciples
Peter and John, as appears from (Luke 22:8) ;

and says to them, go you into the city ;
the city of Jerusalem; for there only the passover might be eaten, (Deuteronomy 26:2) ;

and there shall meet you a man bearing a pitcher of water ;
a servant of the master of the house that was sent for water, to mix with the wine, at the passover:

follow him ;
into the house to which he goes.