God made a decision to give Man free will which He refuses to violate.
How can God bail man out of the mess he is in?
If He chooses armies, the armies will get the credit and be the object of deserved worship. If He chooses angels, the devil can crow that they are evil angels and he then claims the credit. Since God is the only one who can pull this off He must come up with a foolproof way to assure there will be no fraudulent methods of an alternative salvation.
Blood sacrifice is universal choice
The answer is blood. In the 20th century we learn that all blood is personal; each man’s DNA is specific to him/her. From the earliest of times a blood sacrifice for even the most primitive societies has been the offering for the absolution of sins. But how can we certain that this blood of Jesus is unique?
This is the focus of the divine birth of Jesus. The Bible states that the sin passes from father to the children; the mother and her sin is not a factor. So the issue of whether Mary is a sinner is of no consequence.
Sin passes from father to the children
Keeping mercy for thousands, forgiving iniquity and transgression and sin, and that will by no means clear the guilty; visiting the iniquity of the fathers upon the children, and upon the children’s children, unto the third and to the fourth generation.
Therefore, the father of the baby who will save the world must to be sinless; no man can qualify for this job, so God becomes the father. If Jesus did not have a sinless father then Jesus would also be required to die for His own sins.
Mary not considered sinless
The Bible says the Holy Spirit overshadowed Mary and the divine sperm entered her egg. Some religious groups teach that Mary was also sinless as Jesus but clearly this theory is not necessary for salvation, nor is it Biblical.
The sinless Jesus from the sinless father was born 9 months later.
Satan and anyone he chooses to save the world can’t do it because no one he selects is sinless. The result is the One and Only Jesus as the One and Only Savior of the world.
The DNA is the issue and God solved it.
Consequently when ministers say we are saved by the blood of Jesus, they are pointing to the single thing in the universe which can effect salvation and nothing else.