Bible readers are familiar with the idea that Abraham is both the physical and the spiritual father of Israel. Paul expounds this idea very clearly in Romans 9:6-13 and by implication in Romans 2:28f. According to 4:11f., Abraham received circumcision as a sign or seal of his righteousness by faith. The purpose of this, says the apostle, was to make him the father of all who have faith apart from circumcision and likewise the father of those who are not only circumcised but also exercise faith as he did before he was circumcised.
In Galatians 4:21-31 (cf. 3:15-26) the apostle posits two covenants symbolized by Sarah and Isaac on the one hand and by Hagar and Ishmael on the other. If we go back to the source of Paul’s material in Genesis, we shall find that God made both Sarah and Hagar very fruitful. Despite her barrenness Sarah is promised that she will become a mother of nations and that kings will come from her (17:16). And Hagar is also promised great fertility (16:10) even though her offspring will not form part of the covenant people destined to become a blessing to the world (Gen. 17:19-21, cf. 12:3; 18:18, etc.).
In this passage Paul makes another point of fundamental importance to our understanding of Scripture. In distinguishing between Ishmael and Isaac who were both the children of Abraham, he points out that Ishmael was not only born according to the flesh but was in fact a slave by birth. In contrast, Isaac was not merely the child of Sarah the free woman but as the child of promise he also enjoyed ‘spiritual’ birth. (Clearly he was not born again but his birth exceeded the capabilities of his father and mother, and to that extent it was supernatural.) Thus Paul avers that it was the latter, not the former, who would receive the spiritual or eternal inheritance (cf. Heb. 9:15). While the child of the slave woman would eventually be cast out, the child of the free woman, even though he experienced the slavery or bondage of childhood temporarily (4:1), would remain in the house forever (Gal. 4:30, cf. John 8:35).
(Since the Davidic covenant is like the covenant with Abraham a covenant of promise, it is scarcely surprising that David also has two seeds, Solomon and ultimately Jesus who was his greater Son (cf. 2 Sam. 7:13; 23:5; Ps. 89:27-29). They, however, do not have the same typological significance as Abraham’s sons. Jesus was, of course, also Abraham’s seed, Gal. 3:16,18,29)
While this teaching is clear enough, it is not usually appreciated that the notion of physical and spiritual seed goes even further back than Abraham. In Genesis 1 it is emphasized that both the vegetable and the animal world is propagated according to type. While plants yield seed and trees bear fruit in which is their seed (1:12), sea and sky swarm with fish and birds respectively (1:20-22), and the earth produces an abundance of various kinds of animals. Even man himself is urged to be fruitful and multiply (1:28) in his bid to exercise dominion over all creation. Truly is creation both prolific and blessed. But there is a problem. In contrast with the eternal Creator who has neither beginning nor end, creation has a beginning and so is temporal. Furthermore, all creatures great and small are dependent on every green plant for food. And though grass sometimes typifies fruitfulness in the Bible (e.g. Ps. 92:7,12; 103:15), as food it more often symbolizes death (e.g. James 1:10f.). It is not merely perishable as such (John 6:27) but it also guarantees that whatever depends on it is likewise perishable (Isa. 40:6-8). Thus the animals themselves become food that God supplies (Gen. 9:3; Ps. 104:21,27).
It is little wonder then that Jesus is later to say that man cannot live on bread alone but on every word that proceeds from the mouth of God (Mt. 4:4, cf. Dt. 8:3). Here is a hint if ever there was one that man made in the image of God is what the theologians call an anthropological dualism. Though, admittedly, as body and soul he is to be regarded as monistic, as flesh and spirit he is dualistic. If he is to survive beyond this temporal world of which he is a part into eternity and the presence of God, he must, as Jesus told Nicodemus, be born of God (John 1:13f.) from above (John 3:1-8). On the natural level he is like Adam (1 Cor. 15:45-49) and, made in his image (Gen. 5:1-5), he cannot inherit the kingdom of God (1 Cor. 15:50). Only as he is supranatural or spiritual in the image of Christ can he live forever.
In light of all this it is not at all surprising that the NT elsewhere differentiates between two seeds. Peter tells his Christian readers in 1 Peter 1:23 that they have been born again not of perishable seed but of imperishable through the living and abiding word of God. James by implication endorses this comment (1:18), and the author of Hebrews (4:11f.) appears to be on the same wavelength.
In his first letter John also can think in terms of believers in Christ being the offspring of God, not simply in a general or natural (Acts 17:28) but in a spiritual sense. He goes so far as to say that God’s seed (sperma) remains in him who is born again (3:9). This is surely a confirmation of John’s record of the teaching of Jesus in John 3:1-8 (cf. 10:28-30; 1 John 2:19; 5:18). If we are born of the Spirit, we are anointed by him (1 John 2:27) and have him dwelling within us as God’s guarantee (2 Cor. 5:5) and seal (Eph. 1:13; 4:30) of our (eternal) salvation. Truly is God our Father and we his children (1 John 3:1-3, cf. Rom. 8:14-17).
In 2:10 (cf. v.8), however, the apostle goes even further and distinguishes between the children of God and the children of the devil and illustrates his point by reference to Cain and Abel (v.12). It is noteworthy that Jesus had made the same distinction in one of his confrontations with the Jews when dealing with the children of Abraham (John 8;31ff.). On the physical level Jesus is far from denying that those who opposed him were true children of Abraham. On the spiritual plane, however, matters were far different. While they claimed that God was their Father (v.41), they failed to act as if he were. Unlike Abraham who rejoiced to see his day (v.56), they sought to kill the One whom God had sent (vv. 39f.,42). Thus Jesus concludes that their real father was the devil who was a murderer and a liar from the beginning (v.44).
It may be asked at this point what that beginning was. Doubtless Jesus had in mind not the origin of the devil in what was arguably a pre-mundane fall but the encounter between our first parents and the devil. In Genesis 3:15 in what is known as the protevangelium two seeds appear for the first time when God says that he will put enmity between the serpent’s seed and Eve’s, seed. The conflict that began then has raged ever since but, thank God, we as Christians know that the woman’s seed (cf. Gal. 4:4) has in fact bruised the head of the former, and ultimate victory is assured (cf. Mt. 13:37-43).
At the end of the day, our works betray our true origin (Mt. 7:17-20). Those who do what is good imitate Jesus and his Father; those who do evil imitate the devil (3 John 11). Jesus came into the world specifically to destroy the works of the devil (1 John 3:8), and when the purpose of history is finally fulfilled that destruction will be complete. In the universal judgement to come (Acts 17:31; Heb. 9:27), the two seeds will have come to maturity and borne fruit as sheep and goats (Mt. 25: 31ff.) or as the children of God and the children of the devil (1 John 3:10). The former will inherit life in the heavenly city, the latter will suffer destruction outside (Rev. 21:8; 22:15)