Notes on the Bible, by Albert Barnes, , at sacred-texts.com
1 Kings (1 Samuel) 21:1
Nob was a city of the priests, the high priest resided there, and the tabernacle was pitched there Sa1 21:4, Sa1 21:6,Sa1 21:9; Sa1 22:10. It was situated on the road from the north to Jerusalem, near Anathoth, and within sight of the holy city Isa 10:32; Neh 11:32. But the site has not been identified with certainty.
1 Kings (1 Samuel) 21:2
A fresh instance of David's unscrupulous readiness of invention (compare Sa1 20:6).
1 Kings (1 Samuel) 21:4
Common - As opposed to holy. (See the marginal references, and compare the use of the word in Act 10:14-15, Act 10:28.) It gives an idea of the depressed and poor condition of the priesthood at that time, that Ahimelech should have had no bread at hand except the showbread.
1 Kings (1 Samuel) 21:5
The vessels of the young men ... - i. e., their clothes Deu 22:5 or wallets (marginal reference), or other articles which might be Levitically unclean and need cleansing (Lev 13:58; Exo 19:10, etc.; Mar 7:4), as well as the person.
And the bread ... - The meaning is; "Though it is treating it like common bread to give it to me and my young men, there is fresh showbread baked and put on the table in place of what you give us;" the day being Friday. as is indicated in the verse following.
1 Kings (1 Samuel) 21:7
Detained before the Lord - Either to fulfill a vow Act 21:23-27, or on account of uncleanness, or under the law of lepers Lev 13:4, Lev 13:11, Lev 13:21, or as a proselyte. It is not impossible that Doeg may have been in custody or in sanctuary for some crime.
1 Kings (1 Samuel) 21:9
Wrapped in a cloth behind the ephod - Rather, "in the cloak," Goliath's military cloak, which was part of the dedicated trophy. The ephod was naturally hung up where the high priest alone could get at it.
1 Kings (1 Samuel) 21:10
Achish king of Gath - It appears from the title that Ps. 34 was composed on this occasion. (See the note there.) Nothing can give a more lively impression of the straits to which David was reduced than the fact of his going to the country of the Philistines.
1 Kings (1 Samuel) 21:11
The king of the land - The Philistines gave him the title which their own lords bore.
1 Kings (1 Samuel) 21:13
Scrabbled - literally, made marks (margin), namely, the mark of the "tau" (t), which in the ancient Hebrew and Phoenician was in the shape of a cross. (See Eze 9:4.)
On the doors of the gate - The gate of Achish's palace-yard or court, in which the attendants waited. The house itself stood in this court. (Compare Est 2:19, Est 2:21.)