John Gill Commentary Mark 9:2

"And after six days Jesus taketh with him Peter, and James, and John, and bringeth them up into a high mountain apart by themselves: and he was transfigured before them;" — Mark 9:2 (ASV)

And after six days
Six days after this discourse with his disciples, in their way to Caesarea Philippi, and after they were come into those parts:

Jesus taketh with him Peter, James, and John ;
favourite disciples, and a sufficient number, to be witnesses of his transfiguration:

and leadeth them up into an high mountain apart by themselves ;
where he and they were alone. This was not Mount Tabor, as is generally said, but either the mountain which Caesarea was at the foot of, or it may be Mount Lebanon; (See Gill on Matthew 17:1);

and he was transfigured before them ;
the above three disciples; (See Gill on Matthew 17:2).