en_tn/1ch/21/19.md

David went up

This is a reference to elevation. This threshing floor which became the future site of the temple was the highest point in Jerusalem.

as Gad instructed him to do in the name of Yahweh

Speaking "in the name of Yahweh" means speaking with his power and authority, or as his representative. Alternate translation: "as Gad, speaking for Yahweh, instructed David to do" (See: rc://en/ta/man/jit/figs-metonymy)