By chance I read a quote just now tonight.
He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you. —-Friedrich Nietzsche
The “he who fights with monsters” part is fairly straightforward. If you spend your time in conflict with someone or something very horrible, you run a very real risk that you will become just as horrible. For example, if I decide that I will do anything to get revenge on someone who has done something terrible to me, I may do so by doing something equally terrible to them. If someone verbally abuses me, I may feel tempted to equally talk dirty back to them. If you fight with monsters, you can become a monster.
The “abyss” part is more complicated. The best swing I can take at it is this: for Nietzsche, we just are our own consciousness. Our mind is made up of all kinds of thoughts and ideas. When you gaze into an abyss, or in reality spend time contemplating a thing whether is unknown or contrary to us, it changes us.
To put that a little more clearly, our personalities are strongly influenced by what we spend our time thinking about. So if we spend a lot of time contemplating a particular thing, that thing can gradually become a “fixture” in how we behave, how we think and feel. You gaze into the abyss, you get into the abyss, so the abyss finally gets into you as well.
Although Nietzsche does not believe in God, to me it was just like in an instant, that I might feel, or have a new understanding of God’s Grace, along with the reason why we love God and love each other.