John Gill Commentary Mark 12:31

"The second is this, Thou shalt love thy neighbor as thyself. There is none other commandment greater than these." — Mark 12:31 (ASV)

And the second is like
"To it", as in (Matthew 22:39) and so it is read here in two ancient copies of Beza's, and in the Vulgate Latin, Syriac, Arabic, Persic, and Ethiopic versions;

[namely] this, you shall love your neighbour as yourself .
This commandment stands in (Leviticus 19:18) and respects not an Israelite only, or one of the same religion with a man's self, or his intimate friend and acquaintance, or one that lives in the same neighbourhood; but any man whatever, to whom affection should be shown, and good should be done to him, and for him, as a man would have done to and for himself; as much as lies in his power, both in things temporal and spiritual; see the note on (Matthew 22:39) .

There is none other commandment greater than these ;
in the whole law, moral or ceremonial; not the sabbath, nor circumcision, nor the phylacteries, nor the fringes on the borders of the garments, nor any other.