Ambrose of Milan : This digression then of ours from one part of the Law to the other, for the purpose of shewing that the firstborn is not the son of the beloved, that is of the more remiss and voluptuous wife, has not been needless, although the words of the chapter before us express the same truth: He may not make the son of the beloved first-born before the son of the hated, which is indeed the first-born. He is indeed the first-born who is the holy son of a holy mother; true sons do not wander from their true mother, though sinners do wander; the true first-born therefore is he who is the son of the true mother: and he who is not truly the first-born, is strengthened by riches as if he were the first-born, and is honoured that he may not be in want: but he who is truly the first-born receives a double portion of all that he hath, that he may be rich. — Letters 31-40