Charles Ellicott Commentary 1 Chronicles 21:30

"But David could not go before it to inquire of God; for he was afraid because of the sword of the angel of Jehovah." — 1 Chronicles 21:30 (ASV)

But (and) David could not go before it — that is, the Tabernacle at Gibeon and the altar of burnt offering (1 Chronicles 16:4; 1 Chronicles 16:37; 1 Chronicles 16:39).

To inquire of God. — To seek Him, that is, to seek His favour by sacrifice and prayer. (But compare 1 Chronicles 13:3; 1 Chronicles 15:13.)

For he was afraid because of the sword. — “David could not go to Gibeon,” says Keil, “because of the sword of the angel of Jehovah: that is, on account of the pestilence which raged at Gibeon.”

Others have thought that the awful vision of the angel had stricken him with some bodily weakness.

A more natural explanation is that the menacing aspect of the apparition overawed the king, so that he dared not follow the usual course in this instance.

It made, as we might say, an indelible impression upon his mind as to the sanctity of the place where it appeared. (Exodus 3:5; Joshua 5:15; Judges 6:21; Judges 6:26.)