“‘The second commandment is.
‘You shall love
There is no other commandment
Greater than these.’”
δευτέρα αὕτη Ἀγαπήσεις τὸν πλησίον σου ὡς σεαυτόν. μείζων τούτων ἄλλη ἐντολὴ οὐκ ἔστιν.
There is something similar in Matthew, chapter 22:39-40, and Luke, chapter 10:27, but in a more condensed version. This was based on Leviticus, chapter 19:18. A further explanation of the commandments in Leviticus ends with this basic fundamental concept of love your neighbor as yourself, which became the cornerstone of Judaism and Christianity. They were not to hate in their heart anyone of their relatives. They should reprove their neighbor, but not take vengeance on him. They were not to bear a grudge, because they should love them as themselves. Mark said that Jesus replied that the 2nd commandment (δευτέρα αὕτη) was like the 1st one about love. Not only were they to love God, but they were to love their neighbors as themselves (Ἀγαπήσεις τὸν πλησίον σου ὡς σεαυτόν). There were no other commandments greater than these 2 commandments of love (μείζων τούτων ἄλλη ἐντολὴ οὐκ ἔστιν). Everything was based on the love of God and neighbor.