12:29 first of all the commandments. See Deuteronomy 6:4-5. Jesus called this “the first and great commandment” (Matthew 22:38).

12:30 all thy strength. Mark here adds the phrase “and with all thy strength” to the first commandment as given in Matthew 22:37. Probably Matthew, writing mainly for Jewish readers, knew they were more occupied with the heart, soul and mind, whereas Mark, writing more for a Roman audience, and Luke (10:27) thinking of Greeks and Gentiles in general, both retained Christ’s emphasis on strength as well. Both versions are factually accurate, of course, so no problem of inerrancy is involved. The main point in both is certainly that love for God with our whole being is the most important of all rules for living.

12:31 the second. This second great commandment (Leviticus 19:18) is called “the royal law” in James 2:8. See also Romans 13:9; Galatians 5:14.