John Gill Commentary Psalms 119:139

"My zeal hath consumed me, Because mine adversaries have forgotten thy words." — Psalms 119:139 (ASV)

My zeal has consumed me
Zeal for God and his glory, for his word and ordinances and worship; which is a fervour of the mind, burning love, and flaming affections for God, shown in a holy indignation against sin and sinners. This was a zeal according to knowledge, sincere and hearty, and what continued; and which was shown in embracing and defending the truths of the word, and resenting every indignity cast upon them; to such a degree, that it ate up his spirit, wore away his flesh, and almost consumed him; see (Psalms 69:9) ;

because mine enemies have forgotten your words ;
not merely through an indifference to them, and inattention in hearing them; nor through want of an earnest heed to keep and retain them; nor through negligence in laying them up, and a carelessness in making use of proper means to recollect them; but through an aversion to them, an hatred of them, and a spiteful malicious contempt of them, casting them away and despising them; which stirred up the spirit of the psalmist, and raised such an emotion in him as was almost too much for him.