One of the seminal stories of the Bible, Genesis 16 touches on a point in Abram and Sarai's lives before they had children. They'd been living in Canaan for ten years and Sarai was getting anxious for a child. God had promised an heir to Abram so as to begin the lineage that would eventually produce Jesus. Up till now, no child had come. Sarai was barren. So in a moment of worry and weakness she decides to give Hagar, their Egyptian maid, to Abram to preempt the process initiated by God spoken of in the previous chapter. "Lo, children are an heritage of the Lord: and the fruit of the womb is His reward." (Psalm 127:3)
I watched firsthand as my parents' twenty-nine year marriage dissolved day-by-day. Any matrimonial object lessons I've learned were done so by attrition. One mistake after another came to light and as my mom was unwilling to talk about things, my dad realized that he'd married the wrong person. A sad season for all. There's no doubt that Sarai—later known as Sarah—was the one for Abram—whose name is now Abraham. But that model doesn't fit so solidly upon the union that produced my brother and I.
"Be ye not unequally yoked together with unbelievers: for what fellowship hath righteousness with unrighteousness? and what communion hath light with darkness?" (2 Corinthians 6:14)
After Jesus rose from the dead and ascended to Heaven, He left the formation of fledgling church in the Spirit-enabled hands of the Apostles. Paul came alongside to elucidate some of the mysteries concerning the application of Christ-like principles to every arena of their new life as followers of Jesus. One serious point of doctrine is that of Christian spouses living in matrimony with those who are unbelievers. Most of his familial precepts are found in his first letter to the Corinthians. In chapter 7, he tells them to remain with their respective unbelieving spouses, that is, if said non-Christian spouses are "pleased to dwell with them" (verses 11-13). Innumerable stories are told of Christian husbands and wives "travailing in pain until Christ be formed" in their spouse. But what if one member of the marriage is merely pretending to believe while the other who truly does, is oblivious to the duplicity of the non-believer? That's exactly what happened with my mom and dad. And I don't mean to lambast my mother as she is the woman who God used to bring me into this world—physically. But my love for her has turned from that of a son, to that of a fellow human (a Christian at that) who is concerned for, not just her emotional state, but (as a Christian) also her eternal salvation.
"For the unbelieving husband is sanctified by the wife, and the unbelieving wife is sanctified by the husband: else were your children unclean; but now are they holy." (1 Corinthians 7:14)
God took care of Hagar and her son Ishmael after Sarai had cast them out (see Genesis 16:7). To debate on whether or not Sarai's choice to "deal hardly with [Hagar]" (verse 6) was right is not the point here. The point I'm trying to make is, even if you either accept the Lord to your spouse's chagrin, or realize that the person you married is not Christian and not the person you thought they were, take heart. My case is very cut and dry because I really wonder whether or not my mother really loves me. It doesn't bother me anymore. But all of the attendant messiness of divorce can be allayed if both spouses agree to disagree (on such an important topic as religious differences)—because of the children. The children! Can't we please think about the children!? Please do. And if you don't have children yet, think twice. Whereas Paul says that the marriage should remain if both husband and wife are "pleased to dwell" with one another, the topics of disagreement weren't open to discussion in both of my parents' case so they divorced. Cut and dry. The detritus of which took years to sift through.
My brother, ten years my junior, sailed through. I, however, ran aground on the rocky shoal of a marriage that was built upon lies. My late teens and early twenties were rife with the fallout of decisions I made as a child that produced fruit after their kind. My mother's influence of selfishness and deceit led me astray and were it not for my dad's introducing me to Jesus at a young age (four years), I would probably be, now, twice as manipulative as she, ready to continue the cycle.
Isaac was the son of God's promise. Sarah was the wife that God had given to Abraham to produce Isaac. In spite of our tendency to jump the gun and get involved with those we shouldn't, He truly works all things "together for good, to them that love Him, to them who are the called according to His purpose." (Romans 8:28) Everyone's called, not everyone loves Him though.
"For this my son was dead, and is alive again; he was lost, and is found. And they began to be merry." (Luke 15:24)
"As arrows are in the hand of a mighty man; so are children of the youth. Happy is the man that hath his quiver full of them: they shall not be ashamed, but they shall speak with the enemies in the gate." (Psalm 127:4-5)