I Chr 1:28
Ishmael versus Isaac
Paul’s argument in Galatians is to show the recipients of his letter that their desire to serve God by obedience to a written code is a regression back to the type of religion that existed in Israel at the time of writing (Gal 4:21-31). God desired faith in the work of Christ and freedom in service, but their legalistic desires subjected their relationship with God to a works-based righteousness.
Paul goes on to contrast the two children, Isaac and Ishmael, and to bring home to the Galatians that to live according to a legal requirement is paralleled in the birth of Ishmael to Abram, whereas to live in the freedom of Christ parallels Isaac. Though he’s primarily concerned with ‘Law (or Legalism) versus Faith’, there are a couple of verses which can be seen to illuminate God’s purpose in choosing Isaac for the Messianic line rather than Ishmael.
In Gal 4:22-23, the question arises whether the line of promise is through Ishmael according to the flesh or Isaac according to the promise. Though Abram had received the promise from God that He’d be the father of a son who would be his heir (Gen 15:4), he nevertheless decided that the only way God would be able to perform such an act was if he gave Him a helping hand and did something about it while he was still physically capable (Gen 16:1-4,15-16).
However, Ishmael wasn’t the child of promise but a child that had been obtained through self-effort and by attempting to procure the heir ‘according to natural processes’ (a better translation of ‘according to the flesh’ in Gal 4:23), probably using a culturally accepted practice of His day that meant that a slave girl could bear the children of her master and it be considered as if the child was the progeny of the legally accepted wife.
But God made it clear to Abram that Ishmael wasn’t the one God had chosen to perpetuate his line and through whom the Messiah would come (Gen 17:18-19). Even though Abram’s self-effort had produced a child, God was going to give Abram the child according to promise (though still ‘according to natural processes’ but at God’s appointed time when all reasonable chance of obtaining a child demanded a miracle to be performed by God - Heb 11:11-12, Gen 18:11-12) - just as Messiah would be given for mankind through the promise of Gen 3:15 (but through no act of human procreation as in Abram’s case).
So, eventually, Sarah conceived and gave birth to a male child, Isaac, the child of promise (Gen 21:1-4) as it says in Gen 21:12 that
‘...through Isaac shall your seed be named’
(where ‘seed’ can be either singular or plural). God’s choice is more important than our own self-effort - not only when we come to consider the line of the Messiah but also when we look at our own lives before God and the way we expect to see the promises of God fulfilled. The danger for each one of us is that, once we’ve received a promise or assurance that such an event will take place, we go out and, in our own strength, try to make it happen.
Perhaps we even succeed at achieving to some extent what we heard God promise us and ‘give praise’ back to God for the fulfilment of His wonderful promise! But we can fail to realise that what we have is not what God promised at all.
Abram’s self-fulfilment of the promise of God resulted in the Arab nations of the world today, the wholly most antagonistic group of people towards the natural descendants of Abram through Isaac. It may be surprising to us but Abram’s selected fulfilment of the promise (Ishmael) is today violently opposed to God’s choice of fulfilment of the same (Isaac and, subsequently, Israel). We may also find that, should we try and fulfil God’s promises to us, our solution to the problem actually undermines and counteracts the real fulfilment.
God’s eventual remedy to the problem that Abram had brought about was to expel Ishmael away from Abram’s camp, so turning him away from the promise which would be inherited by Isaac (Gal 4:30). But, even so, as we’ve just seen, that wasn’t to be the end of the problem.
Renewing the promise
The confirmation of any covenant needs always to be received in the present, not as a vague promise handed down from father to son.
The Israelites who’d been around at the time of Joshua and who’d seen all the great things that God had done for them as they took possession of the land of promise, stayed faithful to Him until their dying day (Judges 2:6-7). But a new generation arose who hadn’t seen those great works and who didn’t know God personally working in their lives (Judges 2:10).
To them, the stories of God’s great deliverance from Egypt, His sustaining power through the wilderness and His victory on behalf of His people in Canaan were just stories. Therefore, they forsook the ways of God (Judges 2:11-12) and went after other gods - they forgot the promises of God concerning the nation and tried to make their own destiny apart from Him.
God, for this reason therefore, confirmed to Isaac that through him, His purpose for mankind would be realised in Gen 26:4 where it’s recorded that
‘...by your seed all the nations of the earth shall bless themselves’
Though the exact phraseology given to Abram was different (to Abram it was ‘by your seed all the nations of the earth shall be blessed’ which points forward in a more direct way to the One who was to come who would bless the nations of the world), the promise is similar enough to be seen to be a confirmation to Isaac that He was the child of promise and, as such, the one through whom the Messiah would be brought to earth.