This is going to be at least somewhat DM-dependent. In this case, that means you. My advice... make it something meaningful. A Contemplative in particular, has seen an unclouded view of a higher being, and been changed by it in a small but profound way. They seek to cultivate that change in themselves to become more than what they were. Whatever it is, it has to be significant enough that the character can reasonably aspire to further it.
To me, that says that it's a major plot point. It shouldn't be something that the player can just make happen. At most of the levels where the Player might want to be a contemplative, it should be the sort of thing that happens because you, as the DM, decided to make it happen.
It seems that you aren't opposed to the idea of the class in and of itself. If not, you should let this happen. Hopefully, you still have a few levels yet to go before they can qualify for the class and can work it in smoothly.
One way to look at it - by declaring an interest in Contemplative, your payer is declaring that they want their character's story to revolve around a close, personal, deepening relationship with their God. You should give that to them. Give them ways to push the plot towards serving their God more directly. Throw various direct servitors in dire need in their way. Have some other god start stirring up trouble with their god so that there's an excuse for said direct servitors to be in said dire need. They want their story to be all about them and their God, and that's okay (as long as everyone else gets their stories, too). If you run things that way, and you have a couple of levels to work in, they should easily have qualified for the class by the time they want to change to it.
Of course, it's possible that that's not the situation you're in. Maybe the player is already halfway through level 10. In that case... dont' rush it. Act as above, knowing that that means they'll be changing over a few levels late. Then, at some dramatically appropriate moment (not too far down the road) have their God bless them directly by retraining the intervening levels back into Contemplative levels. There's nothing saying that Gods can't do things like that, after all.