Justin Bieber -- I'm on a Mission ... Like an Actual Religious Mission

Justin Bieber is on a self-proclaimed "mission" to learn how to spread the word of God.

Bieber is ensconced in Rancho Mirage outside Palm Springs, where he will spend 2 weeks with a pastor. This Biebs has flirted with religion in the past ... as TMZ first reported he was baptized this past summer in a NYC bathtub.

Bieber has exiled himself from friends, alcohol, weed and everything else that doesn't involve the good Lord.

It's unclear if Biebs will take the next step and become a full-blown proselytizer.

Check out this pic we got of Bieber Monday in Rancho Mirage ... the book by his side is "Occupy All Streets," which teaches how to spread the word and resist bad temptations.

See you in two weeks, Lil Twist!