This extract is from Emes L’Yaakov (R’ Yaakov Kaminetsky) on Shulchan Aruch in the section of the Three Weeks and Tisha B’Av. It seems to me to be a very important and relevant message for today.

Emet L’Ya’akov on Shulchan Aruch OC 551 s.v. Sham

This is what the Torah means when it says “You shall teach them, and guard them to keep them”. In other words a person is obligated to learn the Mitzvot and to know well which are Torah prohibitions, which are Rabbinic, which are fences and which are customs. In other words the ‘guarding to keep’ is only possible through ‘teaching them’. It is not sufficient for a person to watch and copy every action and movement that his father does, even if his father is completely righteous. In such a case a person will not know whether his father is doing the action because it is a Halacha, or just a custom. Through this he will then come to transgress Torah prohibitions, such as causeless hatred and machloket. For this person sees others who are not doing exactly the same things as his father did, he will consider that they are transgressing the Halacha, even though they are also following the minhagim of their fathers. Through this a person will come to transgress ‘You shall love your fellow as yourself’ and ‘Do not hate your brother in your heart’ and ‘Do not make different groups’ which is the prohibition of making machloket according to the Rambam.