The guardian role of gratitude applies not only to prayer and the spiritual battles we fight there, but also to our daily interaction with people. We can see this in Ephesians 5:4. “Let there be no filthiness, nor silly talk, nor levity, which are not fitting; but instead let there be thanksgiving.”
How can we guard ourselves against a foul or frivolous mouth? How can we guard ourselves against a mouth that is foul with criticism and bitterness and blaming and defensiveness and disparagement and resentment and complaining and sarcasm and disrespect and ridicule and cynicism? And how can we guard ourselves against a mouth that is just flippant and trivial and silly and petty? The answer to both questions is, Fill your mouth with thanksgiving.
When a group of people get together and the first people to speak, speak words of gratitude, the conversation seldom degenerates into muck-raking. The group is guarded from sin with gratitude.
John Piper
Website: http://www.desiringgod.org/messages/guard-yourself-with-gratitude