It seems to me that one of the reasons that a moral philosopher might postulate God is that it doesn't make much sense to talk about things being valuable and worthwhile if you aren't prepared to suggest to whom or what they are valuable or worthwhile.
This is where the God of orthodox Christianity comes in handy, because he is by definition the only being who can value everything entirely for its own sake.
But something can be valuable without actually being valued. The kind of worth that’s generally associated with being a person is not the same as the kind that a credit rating agency assigns.
And if things (presumably people) are to be valuable entirely for their own sakes, then the notion of a third-party valuer is pointless: you can’t have intrinsic worth that is externally bestowed. If we need god to impart value to us, then that is subjective worth – and we must all be worthless in ourselves.
And if god values things for their own sakes, then why is a living child more valuable than a dead one? Both are ‘things’ in their own right. To make the distinction you need some criteria of worthiness – and once you have those, they can apply regardless of whether god’s in the picture.
The existence of god is of very little relevance to philosophical questions of worth, morality or purpose.