From St. Bede in the Office of Readings:
Such was the quality and strength of the man who accepted the end of this present life by shedding his blood after the long imprisonment. He preached the freedom of heavenly peace, yet was thrown into irons by ungodly men; he was locked away in the darkness of prison, though he came bearing witness to the Light of life and deserved to be called a bright and shining lamp by that Light itself, which is Christ. John was baptised in his own blood, though he had been privileged to baptise the Redeemer of the world, to hear the voice of the Father above him, and to see the grace of the Holy Spirit descending upon him. But to endure temporal agonies for the sake of the truth was not a heavy burden for such men as John; rather it was easily borne and even desirable, for he knew eternal joy would be his reward.
Since death was ever near at hand through the inescapable necessity of nature, such men considered it a blessing to embrace it and thus gain the reward of eternal life by acknowledging Christ’s name. Hence the apostle Paul rightly says: You have been granted the privilege not only to believe in Christ but also to suffer for his sake. He tells us why it is Christ’s gift that his chosen ones should suffer for him: The sufferings of this present time are not worthy to be compared with the glory that is to be revealed in us.