Bede

When David learned that Saul was secretly planning evil against him, etc. After bringing the ephod with Abiathar, David consulted the Lord, asking whether Saul would come to destroy Keilah, and whether the citizens would hand him over. Hence it can be inferred by what order he consulted the Lord before, that is, by putting on the priestly vestment and thus seeking the Lord's response through the mouth of the priest, and that this was the custom of those consulting God at that time, especially those who could not approach the Ark of …

Commentary on Samuel ↗