19. living … living—emphatic repetition, as in Isa 38:11, 17; his heart is so full of the main object of his prayer that, for want of adequate words, he repeats the same word.
father to the children—one generation of the living to another. He probably, also, hints at his own desire to live until he should have a child, the successor to his throne, to whom he might make known and so perpetuate the memory of God's truth.
truth—faithfulness to His promises; especially in Hezekiah's case, His promise of hearing prayer.