שמואל ב יח:יח פירוש: רש״י

Because he said, "I have no son." That can replace me and be as important as me.⁴He did have children as related earlier (14:27) but did not consider them on a par with his stature. See Sotah 11a.

This will memorialize my name. I will build this stone monument for myself. It was a significant building.