I could be wrong but to me it seems like they could be talking about Jesus's crucifixion. It talks about salvation being "driven in" like the nail being driven into his wrists when he was nailed to the stake, and Jesus is out savior. It would have broke his skin, and he would have bled out, hence the name "bloodwork" and the lines "running red with purpose." Also, "tapping on a grave they call their own." Tapping on the nails they drove into him, put Jesus in the grave, but Jesus saves us from the grave. They also mention it is a "simple test" and "inviting this process". Jesus's death would have been incredibly difficult for him to endure, and he invited the process, because the whole time, he knew this would be coming, and he accepted it freely. Finally, it says "flawless in design". Jesus was a perfect man, flawless in every way. Another idea is that they could be talking about enduring a test in our faith in Jesus's sacrifice. Again, they talk about all the things I mentioned above, but also we would be happy to have our faith tested, to show it is strong. Trials inject themselves into our veins, but we put faith in Jesus's sacrifice and that helps us carry on. We "subject" ourselves to him, letting go of self "pride", and he gives us true purpose and "ignites" is with the power to go on.