Let us learn a posuk with Rashi

Chapter 1:5 verse 3
Hashem is the Master of war; Hashem is His name.

Moshe is looking for the appropriate praise for Hashem in this crucial time. "Master of war" seems to us to be hardly appropriate. There was no "war" for the master of the entire world. Victory over the Egyptians was a non-issue for Hashem. Why is Moshe so taken with the victory in war? 

What does the second part of the verse, "Hashem (in Hebrew yod keh waw keh, the tetragrammaton, or special name of Hashem) actually mean? What insight was Moshe imparting to the people who had just witnessed the great salvation at the sea. Why was the death of the Egyptians so exalting.

Rashi makes several comments.

First, the Hebrew ish means "master" or owner of. Hashem possesses war and has some sort of dominion over it. Rashi brings several examples and the last one is especially instructive.

King David says to Shlomo, his son: ""you will become strong and you will become a man" (l Kings 2:2). The Hebrew ish (man) means, "you will become a man who possesses strength!"

In our verse ish milchama the one who rules war. To the young Shlomo ish, meaning strength. Are these the same?

The second part of the verse Rashi comments: "Hashem does not fight with weapons, but by using his name". What might this mean? How does Hashem fight with "his name"? What is the insight that Moshe is referring to that came as a result of the exodus from Egypt?

Rashi comments further. "this is analogous to David's statement when doing battle with Goliath "You come to me with the sword…and I come with the name of Hashem…" 

Even more difficult: 
How does man (David) fight with the "name of Hashem"? If he means that he is confident of divine support, then he comes to fight with conventional weapons but is aided by Hashem. Rashi makes it appear as though the truth that was stated by Moshe in this verse is referred to by David and that is not possible.

Rashi insists that there is another possible interpretation for this part of the verse. "Even when Hashem is taking vengeance from his enemies, he has mercy upon his creatures, this is the meaning of the name Hashem. This is a remarkable quality not found amongst the kings who walk the earth. When a king is at war he has no other business, and does not have the strength to engage in other things. Hashem wages war and is concerned with the well being of His creation.

When the world was created Hashem created it with a dependence on divine judgment. However, when it became clear that the world could not stand in the face of such a standard, the divine attitude was changed to one of judgment mixed with mercy. Before the punishment was executed Hashem expressed mercy by giving the world untold opportunities to do Teshuva. Moshe knew this and so did the people. Judgment was always tempered by mercy. The punishment was executed only after many opportunities to repent. 

When Moshe appeared before Pharaoh, he knew that the judgment had been rendered. The Egyptians were doomed to their fate before the first of the plagues. They had overstepped and were no longer able to repent. Hashem "hardened their hearts" and they were unable to respond, yet the punishment was delayed until they had refused all the offers from heaven. Moshe in his song of praise about the salvation of the people says I learned a new feature which clarifies the divine interaction with the world. I now understand that even after the decision has been made and the judgment has been rendered, there is still mercy from Hashem. Hashem controls "war" or the process of punishment even after there is no possibility for change. This is what David said to Goliath, and this is what eventually David said to his son Shlomo. Power in every case has to be tempered with mercy. Even when the judgment is clear and appropriate, we continue to be merciful.