1)
Also verse 7 said "when the grass dries, the flower wilts." Why is this repeated?
1.
Rashi (6): This is for contrast to "Devar Elokeinu Yakum l'Olam 1 " - since He lives forever, and can fulfill.
2.
Radak: The matter is repeated to strengthen it.
1
Malbim: This is like it says "Enosh k'Chatzir Yamav k'Tzitz ha'Sadeh...; Ki Ru'ach Avrah v'Einenu...; v'Chesed Hashem me'Olam v'Ad Olam" (Tehilim 103:15-17). Even if many generations passed, Devar Hashem must be fulfilled. It will not delay past the deadline.
2)
What is "Devar Elokeinu"?
1.
Radak: It is what He promised via His prophets.
