Albert Barnes Commentary 1 Chronicles 28:2

"Then David the king stood up upon his feet, and said, Hear me, my brethren, and my people: as for me, it was in my heart to build a house of rest for the ark of the covenant of Jehovah, and for the footstool of our God; and I had made ready for the building." — 1 Chronicles 28:2 (ASV)

My brethren - David retains the modest phrase of a king not born in the purple, but raised from the ranks of the people (see 1 Samuel 30:23; 2 Samuel 19:12). No later Jewish monarch would have addressed his subjects in this way.

The footstool of our God - David views the ark as God’s “footstool” because He was enthroned above it visibly in the Shechinah, or luminous cloud, present from time to time above the mercy seat and between the cherubim (compare related passages).