Paul might have given the answer that the promise was only ever made to those who exercised the faith of Abraham, but instead he actually answers it here slightly differently. In this verse and the following verses he is going to be saying this: ‘God is faithful not only to his promises of blessing, but to his threats of judgment.
The way we should reason when we face some perplexing problem is to start with bedrock principles, and to reason from them. God is faithful is a bedrock principle, and nothing that contradicts it can be true.
We do not vote on truth, as if God’s vote is one, and the votes of unbelieving men and woman count as more than one and outvote God. God is the definition and foundation of truth, and none who say anything to the contrary are speaking the truth; they cannot stand. Therefore, even if the whole human race were allied against God, he would still prevail.
Supposing a father in Edwardian times was very rich and had a splendid home, and suppose many children were born into his family. As the children grew up, he makes this promise. He says, ‘My children, my sons, my daughters, will receive a good education. I will make sure they receive a good education, and that they go into good professions.’ That is the promise, but what happened was that most of the children grew up very proud and arrogant, and very lazy. They certainly went to the university, but most of them were thrown out, because they never did any work, and because they were thrown out, their father did not see them into good professions. Let us say that one appreciated the privilege and the opportunity, and worked, and finally got into a good profession. Then the father adopted other children too, and they were very conscious of their privilege, and they went to university, and they went into good professions. The father’s promise is kept. He never said that he would see all of them in to good professions regardless of how much they applied themselves. He simply said, ‘I will see my sons and daughters get good education and go into good professions.’ Well, he did. He kept his promise, but not to every one of them: in fact, perhaps only to one of the natural children. It is rather like that with the Jews. God’s promise is that his children will be blessed in life and in eternity; not every one of them irrespective of whether they obeyed him or not, loved him or not, sought him or not. God has saved many Jews without doubt in the Old Testament, but always they are called a remnant, a minority. He has saved many Jews at the beginning of the New Testament age, through the preaching on the Day of Pentecost and afterwards. Practically all the very first Christians were saved Jews. And then he adopted other children. He brought in the Gentiles, grafted them in, adopted them, into his true church, and they were saved also. God keeps his promise. Says Paul, ‘You must acknowledge that God is always faithful. It is you who have got the wrong idea in the way and the manner in which he will keep his promises.’ God is justified if he rejects a person, and if you challenge him and if you judge him, he will be perfectly vindicated.
Why is a passage that speaks of God’s judgment brought forward to support his faithfulness to his promise. Are not his promise and his wrath two very different things? Yes, in themselves they are, but both are founded upon the truthfulness of God’s word. It is his truthfulness that means that his promise, once given, can never be revoked, and it is his truthfulness that means that he must punish the guilty and carry out his threats (Hendriksen).