What Chesed is discussed?
Radak: It is benefits that He gives before promising.
Malbim: It is what one does amidst generosity of the heart, without a previous promise, obligation, or do something that he received. It includes words that He does that deviate from nature.
What will be for all generations?
Radak: I will tell Hashem's praise and Emunah to His chosen, so it will be known to the world for all generations.
Malbim: "L'Dor va'Dor" refers to time divided into generations. This applies to Chesed, which is not constant; it is a Chidush that applies in some generations, based on the generation. Even though it looks like natural law is fixed in Shamayim, also nature conducts with hidden miracles to reward or punish. There was a stipulation that the sea split for Yisrael. Also natural conduct is l'Dor va'Dor, i.e. based on the generation.
What Emes will he publicize?
Rashi: You guard Your promise and fulfill Your words.
Malbim: Emunah, or Emes, is what one does amidst obligation, when he promised to do so, or he is obligated due to what he received. Sustaining the world via nature is due to Midas ha'Emunah; since Hashem established laws of nature, it is as if He promised that they will persist all days of the world. E.g. rain will fall in its time, summer and winter will come to in their times.
