I, even I, am the Lord, and apart from me there is no savior. Isaiah 43:11
God is talking about the innumerable times He had saved them in the past. “who makes a way in the sea And a path through the mighty waters, Who brings forth the chariot and horse, The army and the power (They shall lie down together, they shall not rise; They are extinguished, they are quenched like a wick):” (Isaiah 43: 16,17) He is reminding them of His works in saving them and keeping them from all their enemies.
This alone should be suffice, the past, to trust in His power. But God goes on and provides them a promise, that He will save them in the future too. “Behold, I will do a new thing,.. I will even make a road in the wilderness And rivers in the desert.“(Isaiah 43:19)