I've been thinking about Isaac. Genesis doesn't spend a lot of time discussing Isaac, compared to Abraham, Jacob, and even Joseph. But when we turn to the New Testament, Isaac shows up in some interesting ways.
Having spent many years around "brethren", I've heard a lot of talks about types and shadows in the Old Testament, especially in Genesis. I admit that I've become a bit jaded by some of those talks: not everything recorded in the Old Testament has deeper shades of spiritual meaning. But while I say that, I have to admit that the New Testament explicitly describes symbolic meanings in the accounts of Isaac's life.
Galatians 4:21–31 makes the statement that the story of Isaac and Ishmael has "an allegorical sense" (Galatians 4:24). It then goes on to say that Hagar represents the Law, while Sarah represents "the Jerusalem above" (Galatians 4:26). And then it tells us that "the son of the maid servant shall not inherit with the son of the free woman" (Galatians 4:30). The conclusion being that we can't have both law and grace: we need to take our place as those under grace, and eschew putting ourselves under law.
Hebrews 11:17–19 retell the story of Abraham offering up Isaac (Genesis 22:1–19). It tells us that Abraham expected the Lord to raise Isaac from the dead, "whence also he received him in a figure" (Hebrews 11:19). So when we read through Genesis, we're supposed to understand that Isaac died "in figure" on the mountain, and came back down the mountain resurrected "in figure." J. N. Darby points out that the entire character of the promises to Abraham change at the point Isaac is offered:
The promise of the blessing of the nations was not given to Abraham and his seed. It was made to Abram alone in Genesis 12; and so in Galatians 3 we read in the original, "And to Abram were the promises made, and to his seed." So again, the promise which was confirmed before of God to Christ (not in Christ). Hence it is the apostle insists upon its being one, for the promises to Abraham, as father of the Jews, were made in common to him and to his seed together; and it was promised that his seed should be as the stars of heaven, and as the sand which is by the seashore, innumerable. Whereas the promise of the blessing of the nations was given to Abram first, and then confirmed to the one seed, Isaac, figure of Christ sacrificed and risen again, with no mixture of anyone else, nor mention of a numerous posterity. ("Connection of the cross with the entire development of God's ways with man", Collected Writings, Volume 22, pp. 365–372)
It's in Hebrews 11:17 that we read Isaac is Abraham's "only begotten son." This is the only place I can find where that expression is used of someone other than Christ. And here's the amazing part: it's not literally true. Isaac had an older half-brother and several younger half-siblings. He might have been Sarah's only son, but he wasn't Abraham's.
Scripture does this sort of thing sometimes: it makes statements that aren't literally true, and we're expected to understand that they're not literally true. And when that happens, we need to slow down and pay attention. The Scripture is emphasizing a point, and it does so by making us ask, "Wait... what?"
And of course that brings us to Romans 9:6–13 where Isaac's birth, and the birth of his children, are used to demonstrate "Divine, sovereign, individual election". Isaac's place as Abraham's only begotten son is not true in the strictly historical sense, but it's true in God's reckoning. That's really the whole point of the first half of Romans 9.
So I've come full circle, so to speak. When I was much younger, I was eager to see types and shadows in the Old Testament. And then I began to suspect that most or all of that sort of thing was really eisegesis: it's something read into – not out of – Scripture. But now I appreciate that the New Testament does, indeed, support the idea that there are types, shadows, and hidden meanings in the Old Testament.
Now, I don't want to lose sight of an important lesson here. When the New Testament tips us off to some deeper meaning in the Old, we should dive in to see, understand, and appreciate it. But I still view with skepticism some of those interpretations, at least until I can see justification for it in the text. But perhaps that's a rant for another time.