Well, let’s see. First we have to do some work here, I guess
Mark 12:31 The second is this: ‘You shall love your neighbor as yourself.’ There is no other commandment greater than these.”
John 13:34 I give you a new commandment: love one another. As I have loved you, so you also should love one another
What do we think about what? What are you specifically asking here? You’re worried that they’re somehow different?
In the first, Jesus was quoting from the Torah. In the second, he is demonstrating his authority to expand on the ancient command and showing us how we are to love one another. They’re not inconsistent, if that’s what you’re driving at.
You’re riding on top of the large subject of the differences between the Old Testament and the New Testament. Well, they are different. The good news of Jesus Christ is a radical revelation. The old commandment was difficult enough, but the new commandment makes us think even more.
The OT said (Dt 6:4ff) you shall love the LORD your God with all your heart, with all your soul, and with all your strength. Jesus modified this slightly when he said "You shall love the LORD your God with all your heart, with all your soul, with all your mind, and with all your strength.
“Mind” Jesus tells us we must not be legalistic but holy and devout. The OT said that the new covenant would be written on our hearts. We must be fully and unreservedly (in our mind, for example) dedicated to Jesus.
In general, when comparing Biblical texts, our attitude should be of seeking the harmonization of the texts, when possible. Your’s is an example of where Jesus expands on the ancient law given through Moses. Jesus is the “new Moses,” the new law giver.