Albert Barnes on Ephesians 2:4

But God, who is rich in mercy. On the use of the word rich by Paul, Eph 1:7. It is a beautiful expression. "God is rich in mercy;" overflowing, abundant. Mercy is the riches or the wealth of God. Men are often rich in gold, and silver, and they pride themselves in these possessions; but God is rich in mercy. In that he abounds; and he is so rich in it he is willing to impart it to others; so rich that he can make all blessed.

For his great love. That is, his great love was the reason why he had compassion upon us. It is not that we had any claim, or deserved his favour; but it is, that God had for man original and eternal love, and that love led to the gift of a Saviour, and to the bestowment of salvation.