But … I will come into thy house; rather, unto thy house. David, as a layman, would not be entitled to enter within the tabernacle. He would draw near to it, probably bring his offering, and then worship toward it (see the following clause).
In the multitude of thy mercy; or, through the abundance of thy mercy (comp. Psalms 69:13, Psalms 69:16). It was by God's mercy that David lived, that he was maintained in health and strength, that he had a desire to go to God's house, and was permitted to worship there.
Of all these mercies he is deeply sensible. And in thy fear will I worship. David's worship is never without fear—a reverent sense of God's greatness, power, and perfect holiness. Toward thy holy temple.
"David would, according to the custom of the worship then established, turn himself in the time of prayer to the place where the gracious presence of the Lord had its seat" (Hengstenberg; scrap. Psalms 28:2; Psalms 138:7; 1 Kings 8:30, 1 Kings 8:33, 1 Kings 8:38, 1 Kings 8:42, 1 Kings 8:44, 1 Kings 8:48; Daniel 6:10; Jonah 2:4).