Muslims say Jesus is not the seed of David because He is not having any earthly father. But see how the Word of God is perfectly showing us the truth. Jesus Christ is the seed of David to know that you need to read the Bible and understand it very carefully. Eve was made directly from Adam and she does have all the elements that Adam had. Adam had X and Y chromosomes. X and Y are the written codes of God for our body to function. Eve was having doubled the X chromosome. So X from Eve and Y from Adam produced same as Adam. So where is the difference between Adam and his sons? We know that Y chromosome is the one that determines a girl or a boy. But a man has X chromosome also which is passed on to his daughter. So which seed is God talking about? 

A seed is something which has life in it. The purpose of a seed is that it has life in it and will generate a new plant that can produce more seeds of its own kind. But X and Y chromosomes do not have life in it. The one thing that God relates life is with blood. Leviticus 17:14 says “because the life of every creature is its blood. That is why I have said to the Israelites, ‘you must not eat the blood of any creature, because the life of every creature is its blood; anyone who eats its blood must be cutoff.’”. We humans have blood groups also. Generally we talk about the kind of blood flowing in one’s body to relate them with their ancestors. So why cannot it be blood line of David and not X or Y of him that is passed on to his children. Both male and female can carry the blood line of a man. When Jesus said I am Son of Man, and we know from the scriptures that Jesus is born of a Virgin, How is it that He is saying that He is Son of Man? It is because we humans look down upon woman but not God because He has made woman out from Man and so she is also a man. Jesus is Son of God and Son of Man as well. But Jesus says God is Spirit and when the Word of God became flesh in Mary's womb, blood and water from Virgin Mary was used to nourish the embryo in the womb. “In 1 John 5:6 this is the one who came by water and blood- Jesus Christ. He did not come by water alone, but by water and blood. And it is the Spirit who testifies, because the Spirit is the truth.” So Jesus has taken the water and blood from Mary. Mary being the descendent of David is in the blood line of Jesus Christ. Why is Mary’s husband Joseph also shown in the blood line of David is because as Eve was from Adam and had all in common with Him, so is Mary having all in common with Joseph. Matthews 19:4-5 And He answered and said “have you not read that he who created them from the beginning made them male and female and said ‘for this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one flesh.

So the Bible is clear about showing the blood line of both Joseph and Mary to be descendants of David and fulfilling the law of God from the beginning. 

Hence from Bible we are able to see that Jesus is the seed (blood) of David as He is having in Him the blood that was flowing in David.