This verse isn’t God just giving us some good advice - it says that He requires it from His followers. The Hebrew word for requires in this verse means a command or charge, like from a military commander.
So whenever you see injustice, you’re supposed to do something about it - not just look the other way. Or, make up some reason that person doesn’t deserve your mercy - because we’re ordered to be merciful and to love it.
Mercy is the opposite of giving someone what you think they deserve. Sadly, I’ve met people who delight in the punishment of others. Punishments and discipline are necessary, but when we enjoy watching someone get theirs, it’s sadistic not Godly and certainly not humble.
Walking humbly with the Lord isn’t about keeping your head bowed and mouth shut. Walking in humility is about knowing your place and being confident in what you’re supposed to do. A leader is humble when he/she recognizes the gravity and consequences of the actions their people take - and is willing to listen to wisdom. We are all walking humbly when we recognize the opportunities we have to do what is right, and do it without expecting a reward. There are lots of other examples, but I hope you can get the idea.