Exodus 14:13 And Moses said to the people, “Fear not, stand firm, and see the salvation of the LORD, which he will work for you today. For the Egyptians whom you see today, you shall never see again.
Exodus 14:14 The LORD will fight for you, and you have only to be silent.”(emphasis added)
Israel after finally being delivered from Egyptian captivity were forced to face the army of Egypt soon afterward. Pharaoh decided to recapture them since the Jews were in a position they couldn’t escape (Exodus 14:3) 
Instead of showing faith in God the Jews began blaming Moses for their coming death (14:11–12) since there was no way they could defeat the army of Egypt.
The response of Moses was a very big deal because it marked a huge change in the way we face challenges.
The Israelites were used to fighting their own battles (emphasizing human strength or ability) but this time God would fight the battle for them
This truth must have been very encouraging to the Jews, but Moses wasn’t done. He proceeded to tell them they had to be silent.
I happen to like the way this is paraphrased in another Bible version, “GOD will fight the battle for you. And you? You keep your mouths shut!” 
Now obviously Moses isn’t literally telling them to stop talking since a great song of praise to God follows their deliverance (Exodus 15:1–20). So what exactly does Moses mean?
Some commentaries believe this was his way of saying “don’t do anything” but that doesn’t make sense because God questions why the Jews haven’t moved (Exodus 14:15) and they were asked to walk across the red sea (14:21–22).
It’s my personal opinion that God here is demanding the Jewish people obey Him without question. In other words, their responsibility is to trust the Lord.
The Jews had a really bad habit of questioning the commands of God, or complaining about them instead of actually obeying. They were so used to doing things the old way (in their own strength) that this new way (trusting God and obeying) was incredibly difficult.
The crazy thing is I find myself drawn to taking care of things myself (which is much more difficult) just like the Jews instead of just trusting God because obedience means giving up control.
But I’ve learned over the years that trying to do God’s job (fight the battles) is a bad idea, since I make a very poor substitute for God.
“Lord my heart breaks when I think of all the times that I’ve charged into battle only to fail in spectacular fashion, when all you wanted me to do was obey”