NIV Isaiah 45:23 By myself I have sworn, my mouth has uttered in all integrity a word that will not be revoked: Before me every knee will bow; by me every tongue will swear.
In the BibleHub interlinear "before me" seems to be absent (added by the translators) and the person to whom all will bow is not identified:
It seems to read:
"I have sworn by myself, my mouth has uttered in all integrity a word that shall not be revoked: all shall bow the knee to [?] and every tongue shall swear/bless"
Is the implied object YHVH or Cyrus?
NIV Isaiah 45: 14This is what the Lord says: “The products of Egypt and the merchandise of Cush,c and those tall Sabeans— they will come over to you and will be yours; they will trudge behind you, coming over to you in chains. They will bow down before you and plead with you, saying, ‘Surely God is with you, and there is no other; there is no other god.’ ”
This certainly is a very significant messianic prophesy and is the obvious background for Paul's passage in Philippians 2. Of particular note to me is the fact that YHVH says that he will confer on Cyrus an exalted title even though Cyrus does not recognize YHVH (yet) because the conferring is for his own glory!:
Isaiah 45: 4For the sake of Jacob my servant, of Israel my chosen, I summon you by name and bestow on you a title of honor, though you do not acknowledge me. 5I am the Lord, and there is no other; apart from me there is no God. I will strengthen you, though you have not acknowledged me, 6so that from the rising of the sun to the place of its setting people may know there is none besides me. I am the Lord, and there is no other.
God refers to Cyrus as his "shepherd":
KJV Isa 44:28 That saith of Cyrus, He is my shepherd, and shall perform all my pleasure: even saying to Jerusalem, Thou shalt be built; and to the temple, Thy foundation shall be laid.
In addition he refers to Cyrus by the messianic title of "anointed" (ie: "Christ" or "Messiah") and that to him God will open doors that no one will shut:!
NIV 1“This is what the Lord says to his anointed, to Cyrus, whose right hand I take hold of to subdue nations before him and to strip kings of their armor, to open doors before him so that gates will not be shut:
It sounds like he will be more than a king - he will be the Suzerain (Lord)!
Note that God giving Cyrus an exalted title is not intended to glorify Cyrus but to glorify God.
So again, who is the one to whom every knee is bowed in Isaiah 45:23?
Ultimately the Hebrew here is somewhat irrelevant for NT studies since Paul cites the LXX (as usual) and it has an explicit "to me" (EMOI). In light of that and given the context I see it as bowing to God to bow to Cyrus, since it is God who has chosen him by name, anointed him, empowered him, etc.