You can't say, okay, I've loved God and my neighbour now, that's it, done. Tick that one off. Love is the opposite of legalism. Love is a God centred, other person centred, outward looking activity. Legalism is self-centred concern for keeping the rules so as not to make yourself impure, even if at the expense of others.
Legalism is the opposite of Love.
It promotes both spiritual laziness and fear. Spiritual laziness, because it makes you content with mere ritual. You can mask your lack of love with religious acts - going to church, saying the liturgy, taking communion, putting money in the plate. Legalism also promotes fear. But legalism causes fear.