Genesis

But on this introduction of the heir, he necessarily becomes the main subject; and chapter 22 opens with it: "It came to pass after these things," for, indeed, a new scene now opens. The heir of the promise is sacrificed and raised again in figure, and the promise is confirmed to the seed*. The ancient depositary or form of the covenant (even that of promise), mother of the heir (Sarah), now disappears. Abraham sends Eliezer, the steward of his house, to seek a wife for the risen heir, for his only son Isaac, from the country whither Isaac was not to return — in the world such as it is: beautiful figure of the mission of the Holy Spirit, who, fulfilling His office (after the Lord's death and resurrection) with the elect of God who are to form the Lamb's wife in the counsels of God, conducts her (already adorned with His gifts, but waiting the moment when she shall see Him who is heir of all things that belong to His Father) across the desert to her heavenly bridegroom. The call and readiness of the appointed bride is beautifully depicted, and she goes with him, who prefigures the Spirit, to the bridegroom who is heir of all. But mark how false and wretched the position of the espoused wife, if Isaac had lost his hold upon her heart — her home in nature left, and she in the wilderness with one who was nothing to her, if not her guide to Isaac. The walk of the Spirit, moreover, in man, is depicted in the most instructive manner in the details of this history, in the conduct of Eliezer: his simple subjection to what was for him the word of God even when all seemed well (vers. 21-23); heart-reference in thankfulness to God the first feeling (ver. 26); purpose of heart in service (ver. 33), and the like.
{* This distinct confirmation to (not in) the seed, is what the apostle refers to as the one seed, that is Christ. The general promises as to Israel were of a seed as the stars of heaven for number. This is the confirmation to the one seed, when risen, of the promise given in chapter 12.