The Rebbe's guidance on taharas hamishpacha (the laws of family purity) and the mikveh:
A foundation of the Jewish home. Careful observance of taharas hamishpacha brings blessing to the home: in shalom bayis, where difficulties are often rooted in this area (IK 2938, 10938); in being blessed with children and healthy children (IK 2177, 2266, 9168, 10565); and in health and healing, alongside following the doctor (IK 2704, 6132, 6210, 8050). Consult a qualified rav for the practical halachos (IK 9387).
It is never too late to begin. Observance can begin anew at any time, and sincere teshuvah and a renewed commitment bring healing even after past mistakes (IK 2719, 6036, 10664).
Teaching it. Don't let misplaced embarrassment prevent these vital conversations (IK 803). Parents, especially mothers, should speak about taharas hamishpacha with their daughters openly and more than once before marriage, and make sure their children are properly taught (IK 2303, 7999). Present the material in a dignified, professional way (IK 7977).
Building and improving mikvaos. Building a kosher mikveh is vital for the continuity of the community and has an effect for generations; the Rebbe urged communities to build, repair and upgrade their mikvaos promptly, according to recognized halachic experts and with attention to their appearance too (IK 1229, 1230, 1537, 3191, 7694, 7994, 10582). Spreading awareness of taharas hamishpacha and supporting mikveh efforts carries immense merit (IK 1632, 5561, 8741). Concerns about a particular mikveh's standards should not be publicized or used to reject a shidduch over mere suspicion (IK 6933).
See also: Marriage – Peace in the home (shalom bayis).