What is the word 'therefore' there for? The verses prior talk about where fighting comes from.....from our passions and desires. It also says that God resists the proud but gives grace to the humble. Therefore we are to submit to God instead of giving in to these things.
The word submit, according to Strong's Concordance, means this:
"This word was a Greek military term meaning "to arrange [troop divisions] in a military fashion under the command of a leader". In non-military use, it was "a voluntary attitude of giving in, cooperating, assuming responsibility, and carrying a burden"."
I'm guessing in light of the fact that it talks about resisting the Devil ( the enemy) that this is most likely being used in the military fashion. But it could be used either way.
Either way I am to submit to God rather than submit to my fleshly passions and desires.
Why are we to lament, mourn and weep? If you look back at the previous verses, I believe we are to be repentant and mournful about how we have acted in the ways mentioned there. When we repent and mourn our sin, then God will lift us up.