What is "Nes"?
Rashi: It is tests of many afflictions.
Did Hashem already give the Nes?
Radak: He will give to them. Most Nevu'os use past tense in place of future (Radak Yirmeyah 46:23 - for Nevu'ah for the future exists, as if it already came).
Malbim: Yes.
What is "Lehisnoses"?
Rashi: It is to be tested, if they will persist in their Yir'as Shamayim [in spite of many afflictions].
Radak: It is to be aggrandized over our enemies, to raise our flag over them.
Malbim: [A banner] to raise, to gather for war.
What is the meaning of "Mipnei Koshet"?
Rashi: To adorn Your Midos in the world, that when You will give to [Yisrael] good, the nations will not doubt [Your fairness]. Rather, they will affirm Your judgment and say that You properly did good to them, for they stood in many tests.
Radak: Due to Your Emes; You said that You will settle Your nation on their land b'Shalom.
Malbim: You did so to show Your Emes.