Something I never got for religion is if the deity forgives for all of ones sins, why does one have to praise anybody
Again, it depends on the religion and the sect itself.
For many Protestant sects, God isn't requiring of praise, because why would God need anything? Praise is rather an optional, although recommended, act to show appreciation for God.
For others, God only allows those that worship him to enter into heaven, and so praising God is part of that.
Then others, like Catholocism, have concepts like Purgatory, which is basically a minor-version of Hell, where everyone goes to, where their sins are cleaned from them, to allow them to go to Heaven. Praising god means you spend less time in Purgatory.
Then in the non-abrahamic religions, such as Hinduism, praising the gods and performing religious practice is the means by which you are reborn into a good life, and eventually your soul escapes to reconnect to god.
