What is the comparison to the height of Shamayim?
Radak: This is like "Ki Gadol Ad Shamayim Chasdecha" (57:11) - He cannot raise it higher, according to people's view.
Malbim: One cannot associate Shamayim with Eretz at all. One can say that one matter is taller than another only if both have some height. However, Shamayim is tall, and the land is the ultimate lowness! So Hashem's Chesed is overpowered on those who fear Him. It is not based on their level and merit, that one can say that He gave to them more than is proper based on their deeds. Rather, it is absolute Chesed, without any preparation or merit at all for this, for their deeds are the ultimate lowness, and have no value compared to Hashem's Chesed, which is high above high. This explains "Rav Chesed" (verse 8).
Who are "Yere'av"?
Radak: They are Yisrael. Even if they sin sometimes, they all fear Him and repent to Him, unlike other nations, who fear other gods.
