See this explained in the notes at Mark 12:41-44.

The rich men casting their gifts into the treasury - See all this, from Luke 21:1-4, explained on Mark 12:41-44 (note).

And (1) he looked up, and saw the rich men casting their gifts into the treasury.
(1) According to the judgment of God, the poor may even exceed the rich in generosity and liberality.

And he looked up,.... As Christ sat over against the treasury, looking upon the ground, he lift up his eyes; for the treasury was not in an high place, or above Christ, who was right against it. The Syriac, Arabic, and Persic versions leave out this clause.
And saw the rich men casting their gifts into the treasury; See Gill on Mark 12:41.

From the offering of this poor widow, learn that what we rightly give for the relief of the poor, and the support of God's worship, is given unto God; and our Saviour sees with pleasure whatever we have in our hearts to give for the relief of his members, or for his service. Blessed Lord! the poorest of thy servants have two mites, they have a soul and a body; persuade and enable us to offer both unto thee; how happy shall we be in thine accepting of them!

THE WIDOW'S TWO MITES. (Luke 21:1-4)
looked up--He had "sat down over against the treasury" (Mark 12:41), probably to rest, for He had continued long standing as he taught in the temple court (Mark 11:27), and "looking up He saw"--as in Zaccheus' case, not quite casually.
the rich, &c.--"the people," says Mark 12:41 "cast money into the treasury, and many rich east in much"; that is, into chests deposited in one of the courts of the temple to receive the offerings of the people towards its maintenance (2-Kings 12:9; John 8:20).

Saw the rich men that were casting their gifts. For notes on the Widow's Mites, see Mark 12:41-44.

He looked up - From those on whom his eyes were fixed before. Mark 12:41.