Chapter 60, verse 12.
As a Christian, in the light of New Testament revelation, I would interpret Isa. 60 quite differently from you. I see it as prophetic of the New Jerusalem in the Millennial, Rev. 21. Verse 12 of Isa. 60, in keeping with the “new” theme of Revelation, is thus speaking about the new Israel, the new Jerusalem. The covenant would be the new covenant.
Per the Apostle John, “The law was given by Moses, but grace and truth came by Jesus Christ,” John 1:17. Jesus is the truth, the true Israel. As David represented the whole of Israel against Goliath, so Jesus Christ.
Referencing your verse, “For the nation and kingdom that will not serve THEE shall perish,” with all due respect, THEE is Jesus Christ,the Son of God. He alone fulfilled in himself what Israel was supposed to be, but never was.
To the Jews he said, “which of you convinces me of sin.” None of them could. He alone of Israel was sinless and righteous, he alone was qualified to fulfill the righteous demands of the law as the Messiah.
If you respond, I’ll get back with you later as I will be away from the house for a few days.