I think it's because he realized after awhile, all this "game" stuff is obsolete and too much work, when you can just cut to the chase and use your masculine power to take what you want. Girls have rape fantasies anyway, right? And they're attracted to the kind of men who make their own rules, and behave in a dominant way? And they're gonna make rape accusations anyway, and be believed by society when they do; so if you're gonna do the time, hey.
It makes sense that he would turn Christian, then, since Christianity doesn't really have anything to say against rape, as long as the woman wasn't betrothed or married. Roosh is against "fornication" now, but the Greek word translated in the Bible as "fornication" is porneia, meaning harlotry. All he's against, then, is banging sluts and prostitutes, which a lot of men are tired of doing anyway.
Of course, it will be argued, "How am I going to bang young chicks if I'm limited to my aging wife, and can't bang college sluts and whores?" That's where rape and/or seduction of virgins comes in! We can surmise that the Bible allows polygyny, because it says that a man is required to marry any virginal girl that he rapes or seduces. If a man who is already married were not allowed to marry additional wives, then the Bible would have had to provide for the situation where a married man raped or seduces a virgin; but the Bible is silent on that point, indicating it's handled the same way as if he were unmarried.
Another form of rape, of course, is when a woman is compelled by her father to marry a man, and then forced to put out to him. Roosh has said this is desirable.
And, since we know that (1) girls don't need to be educated, (2) girls need to be married off by their mid-teens if their husband is to take full advantage of their 15 magical years of womanhood, and (3) a bride should be virginal, and yet half of girls lose their virginity before age 18, we know that girls need to be forced into marriage before age 18.
Yet, who other than God, or God's church, has the clout to take on the feminists and say that this is the way it needs to be? The secular manosphere got its ass kicked when it tried to bring about such a drastic cultural change. Part of the problem is that the manosphere didn't have the necessary unity; there were still some guys who put their player lifestyle first. Now Roosh is jettisoning them; he's inviting them to self-deport.
Thus, what Roosh is doing is taking the forum in a more dogmatically radically patriarchist direction, and using religion as an organizing force, and as a way of repelling those who aren't serious about fighting against the feminists. Given that it's getting harder to game chicks these days, as more of them go in the direction of spinsterhood, or of choosing men based on their looks in Tinder profiles; plus the fact that he's gotten deplatformed for secular philosophies that perhaps would have been given more protection had they been religious, the direction in which he's gone makes a lot of sense.