Perfectionists not only have trouble forgiving their brothers and sisters 70x7, they have trouble forgiving themselves. And that then makes it hard for them to accept God's forgiveness. They feel that for God to forgive them they must first be perfect as God is perfect, and that's an impossible task. So either they go through life feeling tremendous guilt and seeing God as distant , uncaring and punitive and themselves as worthless failures, or else they feel angry at God for not making a world where it's possible to be perfect. Worse still, they may begin to doubt the very existence of God since they can't see any evidence for a perfect God in this imperfect world.
Perfectionism also affects their relationships with other people.
They begin to expect people to live up to their standard of perfection. Especially, they expect the Church and the people in it to be perfect. But the real world isn't like that. Other people don't have any more chance of attaining perfection than they do. There is no ideal, perfect church.