This verse is taken from one of the most well-known stories in the bible: the Israelite escape from Egypt. You may be thinking by this point in the story the Israelite would have a straight-forward time trusting God, given the miracles and wondrous signs they had witness over recent days in Egypt but they were still having a hard time believing Moses. In front of them stood the great Red Sea: The Red Sea has a surface area of roughly 438,000 km2 (169,100 mi2), is about 2250 km (1398 mi) long and, at its widest point, 355 km (220.6 mi) wide. They saw no way through.
Behind them, they could hear the roaring chariots and foot soldiers chasing them down. They were no match for the Egyptians as they stood amongst men, women and children, young and old.
So Moses had to remind them that no only should they not fear, they should sit back and watch the hand of the Lord go to work. In the most impossible of external circumstances, this is where God sometimes likes to flex His muscles. We must remember as the children of God, we are just that: children. We do not have the oversight or the reach that God does. All He requires from us if for us to be still and know that He is mighty and at the appointed time. He will perform His word in our lives.
Being armed with this knowledge in life is priceless. It should give you the inner peace and confidence to know that no weapon formed against you shall prosper and every tongue risen against you shall be condemned (Isaiah 54:17). The battle has already been won for your sake. Jesus has already shed His blood for you. Do not be afraid, even in this great time of uncertainty, do not let you faith waver. God has always been for you and will always be.
This is the promise and the hope of your future.