Matthew Poole and continuators on Genesis 26:5

5 Because that Abraham obeyed my voice , and kept my charge, my commandments, my statutes, and my Laws.

Here was a covenant made between God and Abraham: and as if Abraham had broken the condition of walking before God required on his part, God had been discharged from the promise made on his part; so contrarily, because Abraham performed his condition, God engageth himself to perform his promise to him and to his seed. But as that promise and covenant was made by God of meer grace, as is evident and confessed, so the mercies promised and performed to him and his, are so great and vast that it is an idle thing to think they could be merited, by so mean a compensation as Abrahams obedience, which was a debt that he owed to God, had there been no such covenant or promise made by God, and which also was an effect of Gods graces to him and in him.