Character Analysis
Before a young Bishop Aringarosa saved this delusional albino monk, Silas had lived a pretty terrible life…a life that's even worse than being delusional.
He murdered his drunken father in his sleep after witnessing his mother's death at his father's hands. He ran away and was forced into hiding because of his appearance, which only strengthened his antisocial proclivities. After having several run-ins with the law over his violent outbursts, he was imprisoned for twelve years in Andorra. Then an earthquake freed him from his cell and he ran away again, starving and half-naked, until he was found and rescued by Aringarosa.
Because Aringarosa's kindness was the first Silas had experienced in basically his whole life, it engendered an undying loyalty. Silas would do anything for the bishop, including murder.
He justifies this blind devotion with religion. His faith in the ultra-conservative Opus Dei allows him to inflict violence upon himself (as well as, you know, to others) as a purging mechanism.
And all things are justified if you're fighting for God:
For the last decade, he had been following The Way, cleansing himself of sins … rebuilding his life … erasing the violence in his past. Tonight, however, it had all come rushing back. The hatred he had fought so hard to bury had been summoned. He had been startled how quickly his past had resurfaced. And with it, of course, had come his skills. Rusty but serviceable.
Jesus' message is one of peace … of nonviolence … of love. This was the message Silas had been taught from the beginning, and the message he held in his heart. And yet this was the message the enemies of Christ now threatened to destroy. Those who threaten God with force will be met with force. Immovable and steadfast. (5.25-26)
His gratitude toward the Bishop for showing him the way to his new hardcore faith gets transferred, partially at least, to the Teacher. He eagerly wants to impress his new benefactor:
The measure of your faith is the measure of the pain you can endure, the Teacher had told him. Silas was no stranger to pain and felt eager to prove himself to the Teacher, the one who had assured him his actions were ordained by a higher power." Hago la obra de Dios," [I do the work of God] Silas whispered, moving now toward the church entrance. (15.7)
In other words, Silas is…loony.
But he's a well intentioned, mislead loon. He regrets the violence he was forced to inflict, but feels that it will all be justified by God. After all, if the good Bishop tells him to do these things, then they can't be wrong…right?
In the end, we actually feel bad for the poor guy. He's merely a pawn in Teabing's grand strategy, and for that he pays the ultimate price.