I'm a former Christian, now atheist, of the agnostic variety, and I find the girl in the painting extremely beautiful. No makeup, natural looks, a little chubby, the epitome of femininity. Those painters of old knew exactly how to capture true feminine beauty. Contrast that image with the current flood of Instagram photos of silicone females with abnormally thick lips, super-sized breasts and exaggerated curves... I won't say "ugly", but I won't say "beautiful" either.
What kind of Christian were you? Catholic, protestant or ortodox?. You can read Chesterton once an atheist and ended up being a Catholic is quite a good lecture and is really rich to learn the religion from other views and not from the normal one. (i dont like fanatics in religion anyways)
Every holy book I've ever read (the Holy Bible, Book of Mormon, Quran, Talmud, cult texts, such as Scientology's, etc.) has made me so repulsed and disgusted by their teachings, that it is impossible for me to even consider accepting their contents as a description of the truth and of how the universe works. I have come to the conclusion that all religions are man-made and tap into the innate human need to belong to a social group and find answers to existential questions. Science is their enemy, as they are based on dogma, rather than scientific, repeatable, verifiable evidence. Science has progressed to a point that their dogmas can no longer satisfy the curious, logical, inquisitive, free mind that seeks irrefutable, fact-based answers. Religions use intuition, sentiment, and false analogies as "proof" of the existence of the divine, and many people, especially those of a lesser educational background, get trapped into them. This is especially true for those who are born into religions, where they are indoctrinated from birth to believe in them and fear the possibility of rejecting them.
The above is not exhaustive or well laid out, I just typed it as it came in my mind.