[Please note that the following does not apply, in the least, to my own family. I love and adore my in-laws.]
As part of my "Parenting from the Torah" series, I'm giving a shiur this Shabbos on "In-Laws". Until I started preparing this shiur, I never realized just how dysfunctional the Tanach's in-law relationships are; they're like step-parents in Disney. Take a look at this list:
• Besuel wants to kill Eliezer and leave Yitzchak unable to wed;
• Rivkah doesn’t even meet her mother-in-law Sarah, but she is expected to fill Sarah's shoes to comfort her husband Yitzchak;
• Potifera tried to seduce Yosef, then imprisoned him (Granted, this was before they became in-laws; perhaps Potifera was all sweetness and light to him afterward… And yes, I'm following Rashi Bereishit 41:45 here, but see Rashbam);
• Lavan abuses Yaakov, then claims all of his property, as well as his wives and children, for himself;
• Yehudah withholds Shelah from Tamar;
• Manoach tells Shimshon not to marry the Plishti woman (Shoftim 14:3, apparently despite her conversion, as noted in Ralbag Shoftim 14:2);
• Shaul wants to keep his daughter from Dovid, and he tries to kill Dovid;
Lest you cite Yisro and Moshe, recall that Yisro makes Moshe promise not to go to Egypt (Nedarim 65a), and to raise his son without bris milah and with an Avodah Zarah education (Mechilta dR' Yishmael Yisro Masechta d'Amalek 1);
And lest you cite Naami and Ruth, note that Naami instantly claims Ruth's baby as her own. Forget parents in-law who tell their children how to raise the grandkids – here Naami decides to raise the child herself!
The animosity continues talmudically, as we are told (Mishnah Yevamos 15:4) that a woman cannot testify that her son has died, to permit her daughter-in-law to remarry – lest she testify falsely just to cause trouble for her daughter-in-law.
And then there's Eruvin 86a, that strife coming from daughters-in-law makes it unlikely that parents will stay with their married sons for Shabbos. Ouch!
Or how about Kalba Savua disowning his daughter for marrying R' Akiva (Ketuvot 62b-63a; note the somewhat variant story in Nedarim 50a)?
Why are the Torah's in-law relationships so sour?
For the full shiur you'll have to be at the shiur, but I'll offer one note here: The Torah's in-law relationships involve a crossing of cultures. Jews marry into Nachorite, Canaanite, Philistine, Egyptian and Moavite families, and cultures are expected to join within one family. Even in the case of R' Akiva and Kalba Savua, it's a class clash of wealthy and indigent. I suspect this carries an important message about what can go wrong in in-law relationships, as well as about what we can do to avoid these problems and build healthy in-law relationships.
And we do want to build healthy relationships. After all, it's important for Shalom, it's important as a display of honour for one's spouse (cf Moed Katan 20b), and it's important because we are obligated to honour our in-laws (Shulchan Aruch Yoreh Deah 240:24).
The lesson isn't necessarily to marry within one's own community, but it definitely includes this: Keep in mind that in all marriages, one community is joining with another, and that requires consideration, flexibility and patience.