Why does Jesus not quote the whole scripture?

Mark 12:28-34

28 One of the scribes came near and heard them disputing with one another, and seeing that he answered them well, he asked him, “Which commandment is the first of all?” 29 Jesus answered, “The first is, ‘Hear, O Israel: the Lord our God, the Lord is one; 30 you shall love the Lord your God with all your heart, and with all your soul, and with all your mind, and with all your strength.’ 31 The second is this, ‘You shall love your neighbor as yourself.’ There is no other commandment greater than these.” 32 Then the scribe said to him, “You are right, Teacher; you have truly said that ‘he is one, and besides him there is no other’; 33 and ‘to love him with all the heart, and with all the understanding, and with all the strength,’ and ‘to love one’s neighbor as oneself,’ —this is much more important than all whole burnt offerings and sacrifices.” 34 When Jesus saw that he answered wisely, he said to him, “You are not far from the kingdom of God.” After that no one dared to ask him any question.

The first commandment that Jesus quotes is the Shema of the Jewish tradition from Deuteronomy 6:4. The second commandment (underlined) is from Leviticus 19:18, but Jesus does not say the entire scripture.


Here is the entire verse - "You shall not take vengeance or bear a grudge against any of your people, but you shall love your neighbor as yourself: I am the Lord."

Why does Jesus not cite the first half of this verse? 

What does it mean for us to understand the "golden rule" without the "take no vengeance" part? 

It seems that we all know that we should love one another. But the fact of the matter is that one person's act of love is another's act of hate. (Also see the language of some people who discuss the future of this country) 

Have we overlooked to basics of what love looks like? At the very basic level love is without vengeance and grudges.