What is an heir in the Bible?

This is used in various applications as of one coming into a possession. It is applied to the Lord when He came to Israel seeking fruit. They said in effect, "This is the heir: come let us kill him, and the inheritance shall be ours." Mark 12:7. Christ is appointed by God to be heir of all things. Heb. 1:2. Believers are by grace made sons through Christ, hence heirs, heirs of God, and joint-heirs with Christ. Rom. 8:17; Gal. 4:7; cf. John 17:22.

None but the children of Abraham inherit the blessing. But this is not the natural seed, but the spiritual. Abraham was the father of the faithful. They who are of faith, the same are the children of Abraham (Gal. 3:7). The natural seed do not count. Abraham is the father of all them that believe, whoever they may be. His line is the line of blessing, and all who believe are on that line; for all who believe are Christ’s, and all who are Christ’s are Abraham’s seed, and heirs according to the promise.

Nor was this all. Another privilege was theirs who were not Abraham's children after the flesh; for as in Christ, being Christ's they were also Abraham's seed, heirs according to the promise (Gal. 3:29.) To get into association with Abraham the Galatian saints saw was needful, but how to accomplish that was the question. Judaizing teachers professed to explain it, insisting on the rite of circumcision and the keeping the law of Moses. Paul showed them the error of all this, and how subversive such teaching was of all Christian blessing, and indeed of salvation itself (Gal. 5:2-4); and told them that they were Abraham's seed already, because they were in Christ. "There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for ye are all one in Christ Jesus. And if ye be Christ's, then are ye Abraham's seed, heirs according to the promise" (3:28-29.)

Verse 29. "And if ye be Christ's, then are ye Abraham's seed, and heirs according to the promise." Christ's, what The members surely of His mystic body, and thus identified with Him spiritually as the seed. The relation of this verse to His earlier reasoning in verse 16 is obvious. Christ personally is the seed of Abraham, in whom alone the promises can rightly take effect. But what originally was not "many," but "one," becomes a number without number as the fruit of the travail of His soul. Believers are the offspring of the one pure corn of wheat, which by the will of the Eternal Husbandman was committed to the ground in death for our sakes. They stand by a common faith in Him who is not only personally the Lord and giver of life, but the beginning also and first-born from the dead, the head of His own body the church (Col. 1:18). In Christ, then, all who believe are positively Abraham's seed; and if so, they are heirs also of necessity and according to the exact tenor of the promise made to Him.

The apostle shows us still greater things. The Spirit we have received is the Spirit of adoption, and we therefore are children. Now he tells us, "If children, then heirs; heirs of God, and joint-heirs with Christ; if so be that we suffer with Him, that we may be also glorified together." For the present we may confine ourselves to the position we occupy as children, as we hope in another chapter to deal with our future condition in the Father's house. All the children then are heirs — heirs of God. It is not only that He has been pleased, in His love and mercy, to bring us into blessed relationship with Himself, but also He has made us His heirs, and, as if even this wondrous unfolding of His grace were not sufficient to satisfy His heart, it is added, "and joint-heirs with Christ." This last clause indeed contains the key to the whole of our blessing. God has associated us with His own beloved Son. He is the firstborn from the dead, and we compose the church of the firstborn through association with Him, and thus are also associated with Him in heirship to all that He Himself, as man, will inherit in virtue of His redemptive work. Every child of God is therefore put into the rank and position of the Firstborn, saving always His own pre-eminence and His own personal and essential dignity. Still as children we rank with Him joint-heirs with Christ. What words could so adequately express the wealth of God's grace, or of the blessedness into which we are brought? For it is not only that He has saved us, brought us to Himself, and bestowed upon us privileges and blessing, but He must, in order fully to satisfy His own heart, put us into the same rank with His beloved Son. Let these words then, "joint-heirs with Christ," have an abiding place in our souls, that we may, by constant meditation upon them, learn ever increasingly what God is in His grace, and what He has done for us through the death and resurrection of our Lord and Saviour; and surely the more we ponder them, the more we shall be led out to investigate and explore the boundless treasure of that inheritance of which we are the heirs, because heirs of God, and joint-heirs with Christ.

Christ is the heir, and we are co-heirs because, and only because, we are associated with Him (Rom. 8:17).

After faith is come, even the believing Jews are no longer under the law. We have put on Christ. We are not before God as sinners in our sins. He only thinks of us as in Christ. He does not see it in us, because it is put away; but we see it, hate it, judge it, though we know it has been judged in Christ. He puts the saints in the place of promise in this way. They are in Christ, and therefore they are the seed of Abraham (v. 29). All the promises find their centre in Christ Himself. The moment I am in Christ, all the promises of God are mine too, and I am come into the full blessing of all the promises of God. "If ye be Christ's, then are ye Abraham's seed, and heirs according to the promise."

It is the Spirit of God in our hearts, the Spirit of His Son within us, that utters this cry, "Abba, Father!" Nothing can ever imitate this cry. Only the Holy Spirit Himself can cry thus in our hearts. This cry, as we have already pointed out, is the proof that He dwells within us. "So," the Apostle adds, "Thou art no longer a slave but a son." Yes, that cry "Abba, Father" is the proof that we are not under law, we are no longer minors, but we are now sons, sons of God. "But if a son, then an heir through God." We are not the sort of an heir that the first verse of our chapter describes, who differs nothing from a slave. We are "heirs of God, and joint-heirs with Christ" (Rom. 8:17). Such is the place to which God brought us when He bought us out from under law.

"Sonship," then, is the word which most fully expresses the nearness and dignity of the place of blessing which is occupied by the saint of today. The word does not actually occur in the Authorized version since the translators preferred to paraphrase it as "the adoption of sons" in Galatians 4:5, and similarly in other places. The whole passage, Galatians 3:21 to 4:7, should be read, when the Apostle's argument will be seen to be that the coming of Christ has inaugurated a new epoch. Before He came the law, with its partial revelation of God, held sway, and believers then were like minors in a family, under a schoolmaster. Having come, and consequently redemption having been accomplished, we are like children come of age, emancipated from the nursery regime and in the full liberty of the Father's house. "Wherefore," says the Apostle, "thou art no more a servant, but a son; and if a son, then an heir of God through Christ" (Gal. 4:7).

In reply the word of the LORD came to Abraham and, as ever with God, His gifts exceed our requests. Abraham had asked for a son, and, in reply, God promises him not only a son but also an inheritance for the seed. Sonship and inheritance are the two great themes of God's reply. The word to Abraham is, "He that shall come forth of thine own bowels shall be thine heir," and, "I am the LORD that brought thee out of Ur… to give thee this land to inherit it." The whole scene illustrates the truth of Romans 8:17, "If children then heirs." Sonship and an inheritance, whether for the earthly people of God or the heavenly, are inseparably connected. Our future prospects are connected with our character as sons. If we are sons, then we must be heirs. God does not have sons without providing for them an inheritance.