The Latin word “gloria” has to do with “glory, fame, renown, praise, honor” among the root concepts are “reputation [and] fame.” This should be considered in connection with the Greek word “μαρτυρια" (marturia), which is the root of the English word “martyr,” but in Greek means “witness, testimony, evidence.”
These ideas suggest that it is the death itself that gives glory to God. This can be understood on a practical level: by dying rather than disavowing his teachings, Peter gave great credence to his testimony as an eyewitness to Christ’s miracles, death, Resurrection, teachings, and Ascension. Peter’s death in itself forms a piece of evidence corroborating the Gospel. Hence, the news of Peter’s death lends credence to the Gospel and increases God’s reputation as the true God and as the Savior of man.
This gives perspective on St. John’s understanding of this line from Revelations: “And they overcame him by the blood of the Lamb, and by the word of the testimony (μαρτυρια), and they loved not their lives unto death.” Revelation 12:11 (Douay-Rheims 1899 American Edition.)
Notice it was the “word” of their “marturias,” which had effect. I suggest that this indicates that the “testimony” should not be taken to be a speech or words. Rather, it was the “word” reporting the testimony – the “news” of their deaths that was effective in spreading the Gospel and saving those who benefit from the “glory” which the death gives to God.
So, the death of each martyred Apostle and of each eyewitness to Jesus’ miracles, death, teachings, Resurrection, and Ascension gives direct evidence of the truth of the Gospel. Further, the death of each Martyr who suffered death rather than disavow what they had heard from the eyewitnesses gives direct evidence of their judgment of the truthfulness and reliability of the eyewitnesses. These deaths therefore aid in the salvation of man, because they give glory – good reputation and fame – which endorse and spread the Gospel as the truth.
In this sense, God’s glory (fame) is a tool of salvation.
Gloria in altissimis Deo.