Praying Without A Pure Tongue

How can one speak before the King of Kings with a mouth which utters forbidden talk? Would not G-d, as it were, respond, "Who is this shameful person who dares to beg forgiveness of his sins with a lowly tongue? Would he dare serve an earthly king with vessels which are covered with grime?" Surely the king would punish him severely for such disgraceful service! How can one contemplate singing the praises of Tehillim before the "One Who spoke and the world came into being" with a tongue which speaks evil talk? Should not one refrain from bringing an unclean object into the Sanctuary of G-d - out of respect for the Glory that dwells there? Can one not feel a sense of shame, having taken that which was given him to serve his Creator, and transformed it into something despicable? Can one hope to seek G-d's favor with a mouth that is impure? Can one transform an accuser into an advocate?

(Rabbi Moshe Alshich of Tzfat)