7:18 David went in and sat before the Lord. Presumably David sat in front of the ark, the symbol of the Lord’s presence (Ex. 25:22; 30:6; Deut. 10:8; Josh. 6:8). It was not usual to sit while praying (Deut. 10:7).
Who am I. Having offered God a house, David is overwhelmed by the Lord’s declaration that He will build David a house. The humility evident in David’s “Who am I” agrees with his recognition that it is the sovereign Lord who has been with him (1 Sam. 16:18 note) to bring him this far.