I know of the teaching that you have heard. The nuts and bolts of it is God was married to Israel.
Israel 45:5
For your Maker is your husband,
The Lord of hosts is His name;
And your Redeemer is the Holy One of Israel;
He is called the God of the whole earth.
At Mt. Sinai was when God made a covenant and married Israel.
Exodus 34:27 Then the Lord said to Moses, “Write these words, for according to the tenor of these words I have made a covenant with you and with Israel.”
But due to Israel's fornication and idolatry over many centuries, God finally had enough and divorced Israel.
Jeremiah 3:8 Then I saw that for all the causes for which backsliding Israel had committed adultery, I had put her away and given her a certificate of divorce; yet her treacherous sister Judah did not fear, but went and played the harlot also.
So on we go to Jeremiah 31 and God making a New Covenant with the House of Israel.
Jeremiah 31:31-32 “Behold, the days are coming, says the Lord, when I will make a new covenant with the house of Israel and with the house of Judah— not according to the covenant that I made with their fathers in the day that I took them by the hand to lead them out of the land of Egypt, My covenant which they broke, though I was a husband to them, says the Lord.
That's all great and dandy, Israel will finally proclaim the Lord as their king and we will live happily ever after. However, there was a problem. God cannot go against his own righteous laws and ordinances. He is bound to them, just as much as God when he was made flesh in Jesus to live a sinless life. So what couldn't God do?
Deuteronomy 24:1-4 When a man takes a wife and marries her, and it happens that she finds no favor in his eyes because he has found some uncleanness in her, and he writes her a certificate of divorce, puts it in her hand, and sends her out of his house, 2 when she has departed from his house, and goes and becomes another man’s wife, 3 if the latter husband detests her and writes her a certificate of divorce, puts it in her hand, and sends her out of his house, or if the latter husband dies who took her as his wife, 4then her former husband who divorced her must not take her back to be his wife after she has been defiled; for that is an abomination before the Lord, and you shall not bring sin on the land which the Lord your God is giving you as an inheritance.
God could not remarry Israel again after he divorced them. That is why God could not remarry Israel again. One of them had to die, and we know it was Jesus who was sent to die for our sins, but to also renew the covenant he had made with Israel. Thus was the greatest love story ever told.
That's the cliff notes of the teaching I believe you are referring to.
Actually, that is very close. Christ will not break His own laws and therefore the marriage had to be dissolved by the death of one or the other. Christ died, thereby dissolving the marriage and freeing Him to marry the church.
Mat 19:3 The Pharisees also came unto him, tempting him, and saying unto him, Is it lawful for a man to put away his wife for every cause?
Mat 19:4 And he answered and said unto them, Have ye not read, that he which made them at the beginning made them male and female,
Mat 19:5 And said, For this cause shall a man leave father and mother, and shall cleave to his wife: and they twain shall be one flesh?
Mat 19:6 Wherefore they are no more twain, but one flesh. What therefore God hath joined together, let not man put asunder.
Mat 19:7 They say unto him, Why did Moses then command to give a writing of divorcement, and to put her away?
Mat 19:8 He saith unto them, Moses because of the hardness of your hearts suffered you to put away your wives: but from the beginning it was not so.
God never intended divorce, it was put into place by Moses because the people did not have God's Spirit and could not fully obey His laws from the heart...
Rom 8:7 Because the carnal mind is enmity against God: for it is not subject to the law of God, neither indeed can be.
Rom 8:8 So then they that are in the flesh cannot please God.
The normal, natural mind cannot be subject to God's law.
carnal:
G4561
σάρξ
sarx
sarx
Probably from the base of G4563; flesh (as stripped of the skin), that is, (strictly) the meat of an animal (as food), or (by extension) the body (as opposed to the soul (or spirit), or as the symbol of what is external, or as the means of kindred, or (by implication) human nature (with its frailties (physically or morally) and passions), or (specifically) a human being (as such): - carnal (-ly, + -ly minded), flesh ([-ly]).
From Bullingers...
Romans 8:7
carnal mind = minding of the flesh, as Rom_8:6.
enmity. Greek. echthra. Here, Luk_23:12. Gal_1:5, Gal_1:20. Eph_2:15, Eph_2:16. Jam_4:4.
against. App-104.
it is not subject to = does not submit itself to. Greek. hupotasso. See Rom_10:3.
neither. Greek. oude.