The dead pull the living down.

With horror he perceived that, by uniting himself as he had with the dead, he had cut himself off from the living. Stripped of all earthly hope, bereft of every consolation, he was rendered as poor as mortal can possiblybe on this side of the grave.

The dead are jealous, jealous, jealous and they will do anything to keep you from the living, the lucky living. They will argue with you, and distract you, and if that doesn't work, they will even let you hug them, and dance for you, and kiss you, and laugh, anything to keep you. The dead are selfish. Jealous. Lonely. Desperate. Hungry. ("The Chambered Fruit")

Value your parabatai," he said. "For it is a precious bond. All love is precious. It is why we do what we do. Why do we fight demons? Why are they not fit custodians of this world? What makes us better? It is because they do not build, but destroy. They do not love, but hate only. We are human and fallible, we Shadowhunters. But if we did not have the capability to love, we could not guard humans; we must love to guard them. My parabatai, he loved like few ever could love, with all and everything. I see you are like that too; it burns more brightly in you than the fire of Heaven

I never saw a dollar bill cry at anyone's funeral.

I do know that for the sympathy of one living being, I would make peace with all. I have love in me the likes of which you can scarcely imagine and rage the likes of which you would not believe. If I cannot satisfy the one, I will indulge the other.