Ps 39:3 My heart was hot within me, while I was musing the fire burned: then spake I with my tongue, KJV
David in his meditations developed a fire in his heart and he did not even have the Spirit indwelling Him as we do. That fire caused by the infusion of the Word and the profusion of the Psalmist's praise made his tongue speak. I am sure it along with the Spirit was what caused the explosion of his Psalms and his zeal for the house of the Lord.
Jer 20:9 Then I said, I will not make mention of him, nor speak any more in his name. But his word was in mine heart as a burning fire shut up in my bones, and I was weary with forbearing, and I could not stay. KJV
Even in persecution, when it seems that the best thing would be is to keep quiet and not give testimony to God; the Word being infused into the heart creates that nuclear fission that cannot allow the mouth to be silent. It has to break forth for the body cannot contain it forever. Oh, my Brothers! May God make us consistently explode into service in a way that make the effects of the bombs in Nagasaki and Hiroshima look like the effects of a match on a redwood!