Dear friends, amongst my brothers I dwell, amongst my people my nation oh Israel how special you are, how pure, how rare, and how needed, how important is your defense and protection.
The secrets of reason itself lays in your mind and the passion of hashem is found in your heart, the keys of the future lie in your land and it's treasure in your service of your creator,
dark clouds cover the landscape and the sorcerers and witches of Olde have gathered to cast a spell on you oh Israel,
yet no spell can be used on the children of Israel, and no harm can befall those who dwell within the clouds of glory, and not on those who "in the name of Israel are called" - hashem has promised Abraham to make him a great nation and to give his children the holy land, yes, all his children, even those who have been lost for some 2 thousand years or more!
Amalek strikes, but who? He strikes outside the clouds of glory, but who straggles along with the children of Israel OUTSIDE the clouds of glory?
Sinners, idol worshipers, the erev rav, Egyptians who cast their lot with the children of Israel and yet are too impure to join the children of Israel in the camp, in the clouds of glory under hashem's direct embrace, and for THEM!
Moses raises his hands to heaven! Directs the children of Israel! GO FIGHT! fight for HASHEM! Fight for the promise hashem has given his children!
When Yisro sees this, that hashem will protect even the stragglers, he decides to cast his lot with Israel "now I know that hashem is greater than all the g-ds".
Hashem did not change his promise ever, even the soldiers of Egypt, they went under the water, and the the water fell on them.
Hashem did not break his promise to Noach. Just as we don't, every time we flush the toilet :)
The children of Israel who were thrown into the Nile river, never died, Yisro saw as Moshe came close, the children came out of the water and followed Moshe home.
But for the Egyptians, hashem counted their evil thoughts as a sin of action! But hashem still found a way, to protect his children and keep his promise both to Avraham, that he will make his children a great nation, and also his promise to noah not to flood the world again.
Now we can begin to understand what is written in the holy Torah and explained by Rashi
"and Yisro heard all that hashem did for the children of Israel, the war of Amalek and the splitting of sea".
Now he knew that his lot with the children of Israel would be locked in for generations to come and that hashem would protect his grandchildren with the children of Israel in a protection of covanent, the promise to Avraham "for to you I give this land" and more.