Answer: That Jesus was Mary’s biological son is a significant biblical assertion. It fulfills prophecy, confirms that Jesus’ birth was truly miraculous, and has strong spiritual implications. At the same time, Jesus was without sin, so many wonder how Jesus could be Mary’s biological son yet be without sin (Hebrew 4:15).

Jesus’ birth is truly miraculous and is prophesied throughout Scripture. The context for what has become known as “the virgin conception” begins in Genesis 3:15. God is judging the serpent for deceiving Eve, and God announces to him that He would put enmity between the serpent and the woman and between his seed and her seed. It is notable that this serpent is identified later as Satan (Revelation 12:9; 20:2), and it is perhaps surprising that the serpent would have “seed.” Perhaps even more surprising, the woman also has “seed” (Genesis 3:15).

In Scripture, “seed” sometimes refers to actual, literal seed, whether for human reproduction or for plants (Genesis 1:29, Leviticus 15:16). However, more often (over 200 times) it is used as a representation of descendants or offspring (Isaiah 48:19, Galatians 3:16). Regardless of its specific meaning in this passage, biological or representative, what is certain is that Eve’s seed would crush the serpent. This foretold of Jesus, who would come and defeat the serpent once for all (1 Corinthians 15:54-57, Revelation 12:9). Jesus was prophesied to be of the seed of Eve, and He fulfilled that prophecy. He also fulfilled the prophecy that He would be of the seed of David (Romans 1:3). Miraculously, Jesus fulfilled many prophecies.

Another prophecy Jesus fulfilled in His birth comes from a prophecy in Isaiah that a virgin would be with child. While the child was still very young, God would give Judah victory over two oppressing kings (Isaiah 7:14–16). It is not clear in the immediate context whether that Hebrew term alma refers to a virgin or simply to a young woman, but it is clear that the prophecy was actually fulfilled by Jesus (Matthew 1:20–23). Jesus was indeed conceived in Mary (Matthew 1:20) and born of Mary (Matthew 1:21) while she was still a virgin (not simply a young woman). Matthew explicitly tells his readers that Joseph kept Mary a virgin until Jesus was born (Matthew 1:24–25). While we often refer to Jesus’ birth by Mary as the “virgin birth,” it is more accurate to understand that Jesus was both conceived in and born from Mary. She was His human mother, and Jesus was conceived in Mary by the Holy Spirit (Matthew 1:18, 20).

It is significant that Jesus is Mary’s biological son for several reasons:

First, as the biological son of Mary, conceived within her and brought forth by her, Jesus could fulfill the prophecy of Genesis 3:15—He was from the seed of Eve.

Second, Jesus could fulfill the prophecy of Isaiah 7:14–16—He was actually born of a woman who was still a virgin. While this is, of course, humanly impossible, it is possible with God (Luke 1:37). The angel explained to Joseph how this would take place (Matthew 1:20–25). Jesus would be conceived by the Holy Spirit, and that would be one of the reasons Jesus would be recognized as the Son of God (Luke 1:35).

Third, the fact that Jesus was not biologically descended from a man is important because Joseph was in the line of Coniah. God had declared that Coniah would not have a descendant rule on the throne of David (Jeremiah 22:24–30). While Jesus was legally Joseph’s son, He was not biologically descended from Joseph. Thus, Jesus was not from Coniah and could fulfill the Messianic prophecies without God breaking His word about Coniah’s descendants.

While the Bible doesn’t provide the details of how the Holy Spirit conceived Jesus in Mary, it is clear that Jesus was born while Mary was still a virgin. That Jesus was Mary’s biological son and Joseph’s legal but not biological son is important and helps us understand how Jesus is able to be a sinless sacrifice for our sins.

So, seeing that Jesus was Mary’s son, conceived in her and born of her, how could Jesus not have had a sinful nature? There are a few theories that try to explain how Jesus could not have inherited a sin nature:

1. Sin nature is passed through the father. The thinking is that since Jesus did not have a biological father, the sin nature could not have been passed down to Jesus. While this has been a traditional view for centuries, it poses some problems. Scripture does not connect the virgin birth with not having a sinful nature. The prophecy of a virgin birth shows that Jesus’ birth would be miraculous, but it stops short of suggesting its theological significance. We should be careful not to apply extra layers of meaning to the virgin birth if those meanings are not clearly identified in Scripture. Also, to say that only men pass on the sin nature could imply that women are less culpable. Mary had a sin nature, not just because her father passed it on to her but because she was a sinner in her own right. Yes, Adam was held accountable for Eve’s sin, resulting in sin and death entering the human race (Romans 5:12, 17), but both were sinners after they sinned. Further, nothing changed biologically for Adam when he sinned, but we know that through this one man, Adam, sin entered the world (Romans 5:12-19). This is a spiritual problem, not a biological one, although sin has impacted biology as well.

2. Had a sin nature but did not sin. The argument says that since Jesus was Mary’s biological son, He received a sin nature, but He did not sin. This poses problems because God could not take on a nature that is contrary to His character. Further, Hebrews 7:26 tells us: “Such a high priest truly meets our need—one who is holy, blameless, pure, set apart from sinners, exalted above the heavens.” Jesus took on flesh but was set apart from sinners. He was tempted in every way that we were yet without sin. And without a sin nature.

3. Conceived of the Holy Spirit and implanted in her. The thinking is that God created a body for Jesus as He did for Adam, and Mary carried Him from implantation to delivery; thus, He was made in the likeness of sinful flesh (Romans 8:3, Philippians 2:7) and still a seed of Mary, although miraculously created.

4. The sin nature is passed on spiritually not biologically. This theory states that sin nature is not confined to human DNA, as seen by the angels that also sinned. Further, the theory states that sin nature is not necessary for sin to occur. Neither Adam and Eve nor the angels had a sin nature, yet they were tempted both internally and externally. Internal temptation can be seen as Satan desired to be like God (Isaiah 14:14) and as the fruit looked pleasing to Eve’s eyes and desirable for gaining wisdom (Genesis 3:6). Externally, the serpent tempted Adam and Eve with fruit and a lie (Genesis 3:4-5). If a sin nature is not required to have the potentiality to sin, Jesus could have been tempted in every way we were without a sin nature, and, as God, was tempted yet without sin. Lastly, sin is a spiritual problem (1 Corinthians 15:22), and eternal life and salvation are spiritual realities passed on spiritually to those who trust in Christ. Therefore, it is not problematic to say that sin nature is passed spiritually and not biologically.

While we may not fully understand how Jesus could not have had a sinful nature, the reality is that Jesus, who was sinless, died on the cross without being a sinner. In order to die and be our perfect sacrifice so we could be saved from sin, He became sin for us (Hebrews 9:28; 2 Corinthians 5:21). Jesus possessed the image of the invisible God (Colossians 1:15). All other men bore Adam’s image, stained with sin, but Jesus—by virtue of the conception by the Holy Spirit—did not. In fact, Paul contrasts Jesus with Adam in Romans 5, explaining that Adam brought death, but Jesus brought life (Romans 5:15–19).