When it is said that we are what we eat, it is just a way of saying that we need to watch what we are eating if we are concerned about our health.
At the very least, we won't want to be eating anything that is rancid or rotten.
In any case, we need to be careful about what we eat because when it goes into our internal system and if it acts up bad, then we can imagine the pain and discomfort.
As much as we must be careful about what goes into our digestive system, then all the more we must be careful about what goes into our spiritual system.
Jesus said that it is what comes out of a man that makes him unclean.
It is from within, from the heart, that evil intentions emerge and make a person unclean and sinful.
But just as how we must watch what we eat in order to be healthy and not to have digestive problems, we too must guard our eyes and our ears from what is bad and evil.
It is by looking at what is impure and listening to what is unclean that our hearts get contaminated by filth and sin.
May the Lord God watch over us and keep us from evil and may we beseech the Lord to keep guard over us so that our lives will be holy and pleasing to Him.