John Gill Commentary 2 Samuel 6:16

"And it was so, as the ark of Jehovah came into the city of David, that Michal the daughter of Saul looked out at the window, and saw king David leaping and dancing before Jehovah; and she despised him in her heart." — 2 Samuel 6:16 (ASV)

And as the ark of the Lord came into the city of David
Being brought there on the shoulders of the Levites:

Michal, Saul's daughter, looked through a window ;
in the king's palace, to see the procession, which was very grand, and in great pomp, attended by a vast number of people, and with music of all sorts. She is said to be Saul's daughter, though David's wife, as having a good deal of her father's haughty temper and disposition, as appears by what follows:

and saw King David leaping and dancing before the Lord ;
the ark of the Lord, by these outward gestures expressing the inward joy of his heart on this occasion;

and she despised him in her heart ;
as acting a mean part, quite beneath himself, and unbecoming his royal dignity.