Garuda Purana is one of the most sacred Mahapuranas for the devout Hindus. It gains importance because of a single factor: It is the only Purana which gives a detailed description of the post-mortem conditions and rituals as believed by this faith. However, it is a belief spread by the dogmatic priestly class.
 
The fact is that the Garuda Purana contains many more details other than these. It reveals the consequences of an action in a very graphical and logical way. While most of the puranas tell one what to do, it also tells us what one should not do!