Albert Barnes Commentary Psalms 39:3

"My heart was hot within me; While I was musing the fire burned: [Then] spake I with my tongue:" — Psalms 39:3 (ASV)

My heart was hot within me – My mind became more and more excited; my feelings more and more intense. The attempt to suppress my emotions only ignited them further.

While I was musing the fire burned – literally, “in my meditation the fire burned.” That is, while I was dwelling on the subject, while I was agitating it in my mind, while I thought about it – the flame was ignited, and my thoughts found expression. He was no longer able to suppress his feelings, and he gave vent to them in words. Compare Jeremiah 20:9; Job 32:18–19.

Then spake I with my tongue – That is, in the words that are recorded in this psalm. He gave vent to his pent-up feelings in the language that follows. Even though there was a feeling of murmuring and complaining, he sought relief in stating his real difficulties before God, and in seeking from Him direction and support.