Answer:
By the blood of Christians, it means the blood and sacrifice of those missionaries and preachers who helped propagate and spread the Good News to everyone. And through their acts of sacrifice, their deaths, the church began to evolve and grow. Thus, it is rightly said that the blood of Christians is the seed of the church.
Explanation:
In Christianity, the believers of Christ who sacrificed their lives in the name of God are called martyrs. And such deaths are considered to be one of the highest forms of showing one's loyalty to God.
So, by the blood of such martyrs, the evolution and development of the church are made possible. Missionaries went to unknown lands, spreading the Gospel to non-believers. And some were killed because of such missionary works. But with the loss of life became the gain in the number of believers who decide to give their lives to Christianity. So, the shedding of blood becomes the 'seed' for the growth and start of a new 'plant' which is the church.
Therefore, the blood of Christians is the seed of the church as it is the 'seed' from which many people began believing in God. Such sacrifice helped in the growth of Christianity, the church.
