A) THE ROOT OF THE ISSUE: TOLERANCE FOR SIN CAUSED BY ARROGANCE IN WORLDLY WISDOM
There is a problem within the Corinthian community that some had taken Paul's words in his previous letter into another extreme; they forbid sex within marriage. Some Corinthians sought to abstain from sex even within marriage as they thought that their spiritual status as Christians are affected by that. That is the main motivation behind 1 Cor 7 as they wrote to Paul regarding Sexual abstinence:
"Now concerning the matters about WHICH YOU WROTE: “It is good for a man not to have sexual relations with a woman.”" - 1 Cor 7:1
Paul had previously warned about sexual immorality (i.e, 6:9), which resulted in a response from the Corinthians to him in a previous letter. Some of the Corinthians with over realized eschatology, thought that they were already in their glorified bodies (4:8), and hence they abstained from Sex even within Marriage (7:1). Paul spent Chapters 1 to 4 to explain to the Corinthians how they were arrogant (4:6-7) with worldly wisdom (3:18-23), and their false spirituality had caused them to condone Sin in their community (5:6-8, 6:8). That is why Paul had to explain in 7:4-5, asking them "Do not deprive one another", because that has resulted in sexual immorality among them (7:2).
B) DIVORCE WITHOUT VALID GROUNDS: DUE TO ABSTINENCE FROM SEX
Therefore Paul's charge towards the Corinthians, is that they are not allowed to divorce based on the wrong believe that "Christians should abstain from Sex, even within marriage". This might have caused some husbands to initiate a divorce due to their wives refusing to have sex with them. That is why Paul went on to say that our bodies belong to each other (7:4), we are not to deprive each other of sex (7:5), a believer couple are to remain married (7:10). And if a wife leaves her husband for invalid grounds as above, she is to remain unmarried or else be reconciled to her husband (7:11)
"To the married I give this charge (not I, but the Lord): the wife should not separate from her husband (but if she does, she should remain unmarried or else be reconciled to her husband), and the husband should not divorce his wife." - 1 Cor 7:10-11
Paul's preferred model is for Christian marriage (Eph 5:22-33), which agrees with Peter (1 Pet 3:1-7) is for the couple to stay together and not divorce each other; Christians are to strive for reconciliation, forgiveness and love, to stay together in marriage by all reasonable means just as Christ loves the Church regardless of her imperfections. So the spouse who had wrongfully walked away from the marriage without valid grounds must "remain unmarried or else be reconciled to her husband".
C) DIVORCE WITHOUT VALID GROUNDS: DUE TO FEAR OF DEFILEMENT FROM UNBELIEVING SPOUSE
Paul as he says in 7:12, that "To the rest I say (I, not the Lord).... ". In these verses, Paul is saying that a believer should stay with an unbelieving spouse, and not leave him. This is due to a misunderstanding that they are forbidden to "yoke with unbelievers" (2 Cor 6:14), so when a pagan turned to a believer, some of them sought to divorce for fear of being defiled by their non-believing spouse. But Paul states the opposite, in that the believing spouse should stick to their marriage so that there is a chance that the unbelieving spouse and children can be saved (7:14).
Christians are to remain in their current status during the time they were called and not seek for a change (7:20). But if an unbelieving spouse initiates a divorce, the believing spouse is not obligated to stop it, and is released from that marriage.
"But if the unbelieving partner separates, let it be so. In such cases the brother or sister is not enslaved. God has called you[
b] to peace. "- 1 Cor 7:15
D) PAUL'S MAIN POINT: DO NOT SEEK A CHANGE IN EARTHLY STATUS
But Paul's main point for this entire section is actually found in 1 Cor 7:17-23. By using Marriage as an example, he further illustrates his main point using Circumcision (v19) and Slavery (v22). His main point is this, let each man seek NOT to change their social status at the time they were called.
"Only let each person lead the life[
c] that the Lord has assigned to him, and to which God has called him. This is my rule in all the churches." - 1 Cor 7:17
This is consistent with his view in Col 3:2, "Set your minds on things that are above, not on things that are on earth". Since Slaves are considered freeman in Christ, and freemen are considered Slaves to Christ (Rom 6:17), Paul is saying regardless whether one is married or single (7:1-14), circumcised or uncircumcised (7:15-19), Slave or Free (7:20-24), all are the same in Christ, and one's social status does not affect one's spiritual status.
Therefore this is the whole point of the entire section: "Each one should remain in the condition in which he was called " - 1 Cor 7:20
E) APPLICATION: COMMAND VS CONCESSION
Hence to appropriate this to Christian Marriage, Paul commands Christians to stay together and not to seek alternatives and use Divorce and Remarriage as an excuse to legalize their unsatisfied lusts. However, no where in these passages does Paul addresses specific circumstances whereby abandonment, abuse and adultery are involved (Matt 5:32, 19:9). Many Christians had unnecessarily applied a blanket rule that forces believers to continue in hurtful abusive relationships and remain single when the bible states no such command.
Therefore the Sin relating to Divorce and Remarry, is not in the act by itself, but stems from an unwholesome motivation behind such decisions. At the end of the day, it is God who knows our every thoughts and motives (Psalms 139:1-4). This is not a command for all Christians to have to remain status quo, but for each believer not to actively set their mind to seek for a change in their social status in the world, but to stay faithful to their calling in Christ (7:17), wherever God has placed them (7:18).
But in circumstances whereby one does not have a gift of celibacy, or there is abuse and abandonment involved, there is concession. But the believer spouse must have exhausted all means to salvage the relationship, because God had never meant for the Christian marriage to come apart (Matt 19:3-8), but for believers to stand firm to the end (Eph 5:25).