“Christians who divorce and remarry...”
You are correct. Most divorce is sin. Though not unforgivable.
Christ is no rainbows and unicorns moderate, He is hard line G-Party all the way.
He explained to the establishment types of His day (Pharisees,etc.) that God never approved of divorce except in the case of a cheating spouse. Casual divorce was NOT revealed wisdom, but rather an earmark which Moses tolerated to appease the drifting base and Leftward lobbying ACLU (Always Clamoring for Levitical Unraveling).
Moses made more than one mistake in God’s eye. And despite all the incredible work and faith of Moses, God still punished him (no promised land). Kinda makes a fellow take stock, ya know.
God views adultery as analogous to idolatry. Leaving one’s primary love for another. Very bad. He does not like being dumped anymore than earthly spouses do.
Christ teaches on multiple levels. And we’d be wise to consider what He was teaching that day regarding, as He mentioned, the hardness of hearts.
Spiritual wanderers should not expect a letter of commendation from Him for thinking outside the tabernacle. But, without repentance, they might see divorce papers from God.
Of course, we’ve got the best Jewish Lawyer money can’t buy in Christ so we’ve always got a fighting chance. But He does not work on retainer.
Based on Mark 10, all divorce and remarriage is a sin.