"By faith Abel offered unto God a more excellent sacrifice than Cain, through which he had witness borne to him that he was righteous, God bearing witness in respect of his gifts: and through it he being dead yet speaketh" (Hebrews 11:4).
Since the earliest years of this earth's history, the blood of martyr's has been the seed that spreads the truth of God's character and influences the living to trust in Him.
Abel was a steadfast adherent to the will of God. More than anything else, he wished to exalt his Maker as the Supreme One, as the Master of all that is. By sacrificing one of his choice lambs for a burnt offering to the Lord, this younger son of Adam was looking ahead to both the Father's immense pain in separating from His Son in a gift to the world; and Jesus' immeasurable sacrifice.
Though an imperfect reflection, it was indeed "a more excellent sacrifice than Cain." It was heart service. Abel believed in his heart that a Messiah would come and save the human race. And by this faith, he proved was what in his heart -- righteousness.
Yet for this righteousness, for this full belief in God and His gospel, for this distrust in self, Abel was slain. Through jealousy and broken pride was this deed done. But "he being dead yet speaketh."
How, since the dead know not anything? By his blood. Coming to the murderer, the Lord said, "The voice of thy brother's blood crieth unto me from the ground."
Every drop of blood slain for the great cause speak in favor of the blood of Jesus Christ. He was the greatest martyr; and every casualty of the cross following His will be a witness to that sacrifice and what it bought for mankind.
In apostolic days...
"In the providence of God, Peter was permitted to close his ministry in Rome, where his imprisonment was ordered by the emperor Nero about the time of Paul’s final arrest. Thus the two veteran apostles, who for many years had been widely separated in their labors, were to bear their last witness for Christ in the world’s metropolis, and upon its soil to shed their blood as the seed of a vast harvest of saints and martyrs."*
...and in the days of the Reformation.
"The work of these missionaries began in the plains and valleys at the foot of their own mountains, but it extended far beyond these limits. With naked feet and in garments coarse and travel-stained as were those of their Master, they passed through great cities and penetrated to distant lands. Everywhere they scattered the precious seed. Churches sprang up in their path, and the blood of martyrs witnessed for the truth. The day of God will reveal a rich harvest of souls garnered by the labors of these faithful men. Veiled and silent, the word of God was making its way through Christendom and meeting a glad reception in the homes and hearts of men."**
But as the time approaches that Jesus should come, the blood of martyrs will no longer bear fruit unto righteousness. Every case would be decided; every soul would have made his choice. It will be too late. The voice of martyr's blood will cease their crying, and those who have made their choice against the truth will be without hope. Then, God's people will be spared from the sword.
"The eye of God, looking down the ages, was fixed upon the crisis which His people are to meet, when earthly powers shall be arrayed against them. Like the captive exile, they will be in fear of death by starvation or by violence. But the Holy One who divided the Red Sea before Israel, will manifest His mighty power and turn their captivity. 'They shall be Mine, saith the Lord of hosts, in that day when I make up My jewels; and I will spare them, as a man spareth his own son that serveth him.' Malachi 3:17. If the blood of Christ’s faithful witnesses were shed at this time, it would not, like the blood of the martyrs, be as seed sown to yield a harvest for God. Their fidelity would not be a testimony to convince others of the truth; for the obdurate heart has beaten back the waves of mercy until they return no more. If the righteous were now left to fall a prey to their enemies, it would be a triumph for the prince of darkness. Says the psalmist: 'In the time of trouble He shall hide me in His pavilion: in the secret of His tabernacle shall He hide me.' Psalm 27:5. Christ has spoken: 'Come, My people, enter thou into thy chambers, and shut thy doors about thee: hide thyself as it were for a little moment, until the indignation be overpast. For, behold, the Lord cometh out of His place to punish the inhabitants of the earth for their iniquity.' Isaiah 26:20, 21. Glorious will be the deliverance of those who have patiently waited for His coming and whose names are written in the book of life."***
*Excerpt from Acts of the Apostles, p. 537
**Excerpt from The Great Controversy, p. 71
***Excerpt from The Great Controversy, p. 634