21 (For those priests were made without an oath; but this with an oath by him that said unto him, The Lord swore and will not change, you are a priest forever after the order of Melchizedek:)
Hebrews 7:21 Cross References - KJ2000
1 Samuel 15:29
29 And also the Strength of Israel will not lie nor repent: for he is not a man, that he should repent.
Psalms 110:4
4 The LORD has sworn, and will not relent, You are a priest forever after the order of Melchizedek.
Hebrews 6:16-18
16 For men verily swear by the greater: and an oath for confirmation is to them an end of all strife.
17 So God, willing more abundantly to show unto the heirs of promise the immutability of his counsel, confirmed it by an oath:
18 That by two immutable things, in that it was impossible for God to lie, we might have strong encouragement, who have fled for refuge to lay hold upon the hope set before us:
Hebrews 7:17
17 For he testifies, You are a priest forever after the order of Melchizedek.