John Wesley on Deuteronomy 13:6

The son of thy mother - This is added, to restrain the signification of the word brother, which is often used generally for one near a - kin, and to express the nearness of the relation, the mother's, side being usually the ground of the most fervent affection. Thy daughter - Thy piety must overcome both thy affection, and thy compassion to the weaker sex. The father and mother are here omitted, because they are sufficiently contained in the former examples.