John Calvin Commentary Exodus 3:8

"and I am come down to deliver them out of the hand of the Egyptians, and to bring them up out of that land unto a good land and a large, unto a land flowing with milk and honey; unto the place of the Canaanite, and the Hittite, and the Amorite, and the Perizzite, and the Hivite, and the Jebusite." — Exodus 3:8 (ASV)

And I am come down to deliver them. He now more clearly announces His intention not only to relieve their present calamity but also to fulfill the promise given to Abraham regarding the possession of Canaan. He therefore indicates the purpose of their deliverance: that they might enjoy the rest and inheritance promised to them.

It is a common way of speaking to say that God "descends" to us when He actually exercises His power and shows that He is near us. This means that the Israelites would clearly experience that His help was at hand.

The "large" land seems to be contrasted with the difficult circumstances in which they then found themselves. For although the land of Goshen was fertile and convenient, it hardly provided enough space for their increasing multitude. Moreover, they were kept confined there like slaves in a house of bondage.

Finally, He again assures them that He would deal graciously with them, because He had heard their cry and was not ignorant of their sorrows, even though He might have long delayed in avenging them.