God could have chosen to have the Red Sea all dried by the time the children of Israel arrived. They would have walked across and basically disappeared from sight. Believing in magic and mysticism, Pharaoh would have explained it away claiming Moses performed some trick. Instead God chose to allow Pharaoh to be right on their heels before making a way when no one could see a way. He allowed the enemy to view the glory and power of God at work in the lives of His people. Not only did the children of Israel experience another miracle of God's hand but the enemy also had to witness it so everyone would know that it was God and only God!
Even after witnessing the power of God, the enemy didn't stop pursuit. Had they turned back at that moment, then they would have been spared. The problem with that is that Pharaoh would have just tried to find another way to attack, harass and hurt and kill the children of Israel. God allowed them to keep coming until HE said no more. While God was preparing a way out of trouble for His people, He was also creating the trap for the enemies demise.
So if you are standing at your Red Sea with the enemy on your trail, just lift your hands to God and ask Him to make a way because you can't see a way. He is more than willing and able to not only deliver you from the enemy but He will stop the enemy from ever coming for you again.