Галатам 3:29

and heirs--The oldest manuscripts omit "and." Christ is "Abraham's seed" (Gal 3:16): ye are "one in Christ" (Gal 3:28), and one with Christ, as having "put on Christ" (Gal 3:27); therefore YE are "Abraham's seed," which is tantamount to saying (whence the "and" is omitted), ye are "heirs according to the promise" (not "by the law," Gal 3:18); for it was to Abraham's seed that the inheritance was promised (Gal 3:16). Thus he arrives at the same truth which he set out with (Gal 3:7). But one new "seed" of a righteous succession could be found. One single faultless grain of human nature was found by God Himself, the source of a new and imperishable seed: "the seed" (Psa 22:30) who receive from Him a new nature and name (Gen 3:15; Isa 53:10-11; Joh 12:24). In Him the lineal descent from David becomes extinct. He died without posterity. But He lives and shall reign on David's throne. No one has a legal claim to sit upon it but Himself, He being the only living direct representative (Eze 21:27). His spiritual seed derive their birth from the travail of His soul, being born again of His word, which is the incorruptible seed (Joh 1:12; Rom 9:8; Pe1 1:23). Next: Galatians Chapter 4

The apostle in this chapter, I. Reproves the Galatians for their folly, in suffering themselves to be drawn away from the faith of the gospel, and endeavours, from several considerations, to impress them with a sense of it. II. He proves the doctrine which he had reproved them for departing from - that of justification by faith without the works of the law, 1. From the example of Abraham's justification. 2. From the nature and tenour of the law. 3. From the express testimony of the Old Testament; and, 4. From the stability of the covenant of God with Abraham. Lest any should hereupon say, "Wherefore then serveth the law?" he answers, (1.) It was added because of transgressions. (2.) It was given to convince the world of the necessity of a Saviour. (3.) It was designed as a schoolmaster, to bring us to Christ. And then he concludes the chapter by acquainting us with the privilege of Christians under the gospel state.

3:29 Because Christ is the ideal descendant of Abraham (3:16), it follows that those who are one with Christ (3:27-28) are children of Abraham and heirs of all that was promised to him.