“The Jews erroneously imagined (as modern Dispensationalists do) that the promises made to Abraham concerning his seed respected all of his descendants. Their boast was “we be Abraham’s seed” (John 8:33), to which Christ replied, “If ye were Abraham’s children ye would do the works of Abraham” (verse 39 and see Romans 4:12). God’s rejection of Ishmael and Esau was decisive proof that the promises were not made to the natural descendants as such. The selection of Isaac and Jacob showed that the promise was restricted to an elect line. “The children of the flesh, these are not the children of God; but the children of the promise are counted [regarded] as the seed. For this is the word of promise. At this time will I come, and Sarah shall have a son (Romans 9:8, 9) . The “children of God” and the “children of the promise” are one and the same, whether they be Jews or Gentiles. As Isaac was born supernaturally, so are all of God’s elect (John 1:13). As Isaac, on that account, was heir of the promised blessing, so are Christians (Gal. 4:29; 3:29). “Children of the promise” are identical with “the heirs of promise” (Heb. 6:17, and cf. Romans 8:17).
God’s promises are made to the spiritual children of Abraham (Romans 4:16; Gal. 3:7), and none of them can possibly fail of accomplishment. “For all the promises of God in Him [namely Christ] are yea, and in Him amen” (2 Cor. 1:20). They are deposited in Christ, and in Him they find their affirmation and certification, for He is the sum and substance of them. Inexpressibly blessed is that declaration to the humble-minded child of God – yet a mystery hid from those who are wise in their own conceits. “He that spared not His own Son, but delivered Him up for us all, how shall He not with Him also freely give us all things?” (Romans 8:32). The promises of God are numerous: relating to this life and also that which is to come. They concern our temporal well-being, as well as our spiritual, covering the needs of the body as well as those of the soul. Whatever be their character, not one of them can be made good unto us except in and through and by Him who lived and died for us. The promises which God has given to His people are absolutely sure and trustworthy, for they were made to them in Christ: they are infallibly certain for fulfillment, for they are accomplished through and by Him.”
– A.W. Pink (source)