Is there a word for "one who has never sinned"? I can think of "innocent" of course, which means "free from sin or blame" except that it doesn't include the emphasis on not having sinned ever in the past.
That word is immaculate, as in immaculate conception. Per the OED, it means
Free from spot or stain; pure, spotless, unblemished, undefiled. In fig. senses.