Why did the Catholic Church become powerful in western Europe?

In the middle ages much the concern was with the afterlife, as opposed to the current one so religiously the Church held a lot of power. The Church held power over your very soul - commoner or nobleman. Eventually that power was used to collect taxes and tithes which in turn created more power and influence. Along with it came corruption, when religious titles/positions could be given/purchased, indulgances sold, etc.