Devotion or loyalty to a person, group, or cause.
Allegiance
To express a personal conviction. To make a statement based on personal knowledge or belief : bear witness.
Testify
A formal statement of religious beliefs. An organized religious body having a common creed.
Confession
An experience associated with the definite and decisive adoption of a religion
Conversion
A person who voluntarily suffers death as the penalty of witnessing to and refusing to renounce a religion.
Martyr
Matthew 10:32
So everyone who acknowledges me before men, I also will acknowledge before my Father who is in heaven,