The phrase recalls Old Testament promises as contained in 2 Samuel 7:14 and Psalm 89:26–27. More specific to the present context, however, is the earlier use of the word “heritage” (literally, “inherit”). It is commonly sons who inherit their father’s possessions (see Numbers 36:1–13). By designating these people as “sons,” the Lord is building on the earlier notion of inheritance. The passage is family language.
7 The one who conquers will have this heritage, and I will be his God and he will be my son.