就算你想用引伸义，也该用“坚定的”，而不是“忠实的”。
且不说原文里的宗教意味，岂是能用现在的用法说明的？
sworn
–verb
1.    pp. of swear.
–adjective
2.    having taken an oath: a duly elected and sworn official.
3.    bound by or as if by an oath or pledge.
4.    avowed; affirmed: He is my sworn enemy.

Based on the Random House Unabridged Dictionary, © Random House, Inc. 2006.

sworn (swôrn, swrn) Pronunciation Key Audio pronunciation of "sworn" [p]
v.
Past participle of swear.
adj.

1. Having been asserted as true under oath: sworn statements by witnesses.
2. Bound or empowered by an oath: a sworn official.
3. Avowed: a sworn friend.

The American Heritage® Dictionary of the English Language, Fourth Edition
Copyright © 2000 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.