Exodus 14:31 And Israel saw that great work which the Lord did upon the Egyptians: and the people feared the Lord, and believed the Lord, and his servant Moses.
The one great work of God, the miraculous Crossing of the Red Sea, was a work of both judgment and salvation: Judgment upon the Evil Enemy, Salvation for the people of God. The same water saved the one and destroyed the other. The same result occurred at the Great Work of God in the Cross and the Tomb: Judgment upon our spiritual enemies and salvation for us. This same Event prefigures our Baptism and our daily remembrance of baptism: the old man drowns and the new man arises.
Two opposite responses result from this great Event: FEAR! 1) Fearing God with the meaning of being afraid of God’s wrath and judgment without knowing love and mercy: Ex. 14:25 ”The Egyptians said, Let us flee from the face of Israel; for the Lord fights for them.” And 2) Fearing God in the proper sense of believe God, being in awe of amazing grace and abounding love: Ex. 14:31 ”The people feared the Lord, and believed the Lord.”
Which kind of fear one responds with depends on which side he’s on. If one is on the side of well-deserved judgment, without faith in mercy, he will flee. Fleeing takes different forms: rationalizing actions, excusing behavior, defying God, ignoring God’s Word, or just stubbornly refusing to believe, atheism, false doctrine, idol religions, keeping Self on the throne in place of God. If one is on the side of undeserved salvation, with faith in grace, he will believe.
Faith (fear) comes after they ”saw that great work which the Lord did.” After we see the great work of judgment and salvation that the Lord did on the Cross we believe. And we can see the cross and hear the Gospel every day. Then faith comes.