Hebrews 7:17 also quotes Psalm 110:4, but 7:21 adds the oath to emphasize the permanence of Christ's priesthood.

Hebrews 7:11 questions the need for a new priesthood, setting up the contrast with the oath-established priesthood in 7:21 that replaces the Levitical order.

Hebrews 7:16 describes Christ's priesthood based on indestructible life, which the oath in 7:21 then confirms and seals.

Hebrews 7:28 contrasts weak priests under the law with the perfect Son consecrated by the oath, summing up the point of 7:21.

In Hebrews 6:16-18, God's oath confirms his unchangeable purpose. This provides the theological framework for the oath in 7:21 that makes Jesus' priesthood permanent.

Hebrews 5:6 quotes the same Psalm 110:4 about a priest forever. It introduces the verse that 7:21 later elaborates with the oath.

Hebrews 6:18 emphasizes God's immutable oath, reinforcing the unchangeable nature of the oath in 7:21 that establishes Christ's eternal priesthood.

Psalm 110:4 is the source of the oath quoted in Hebrews 7:21: 'The Lord has sworn, You are a priest forever.'

Psalm 89:3 records God swearing an oath to David. Like 7:21, it involves a divine oath establishing a perpetual figure, though for a king, not a priest.

Acts 2:30 mentions God's oath to David about a descendant on his throne. Both passages highlight a divine oath establishing an eternal figure, king vs. priest.