John Gill, on Lam 3:51

Thou hast heard my voice,.... Either in times past, when he cried unto him, and was delivered; and this was an encouragement to call upon him again in such extremity, who had shown himself to be a God hearing and answering prayer; hence it follows: hide not thine ear at my breathing, at my cry; turn not a deaf ear to me, who hast been wont to hear me heretofore; stop not thine ear at my cry now, at my prayer, which he calls his "breathing"; prayer is the breath of a soul regenerated by the Spirit, and is a sign and evidence of life, when it is spiritual; in it a soul pants after God, and communion with him, and salvation by him. Some render it, "at my gasping" (s); or "panting", for breath; just ready to expire, unless immediate help is given: or else the whole of this refers to the present time, when the Lord heard and answered, not only the first clause, but this also; which may be rendered, not by way of petition, but affirmation, "thou didst not hide thine ear at my breathing, at my cry" (t); and this agrees both with what goes before, and with what is expressed in Lam 3:57. (s) "ad anhelitum meum", Cocceius; "ad respirationem meam", Pagnius, Montanus, Junius & Tremellius, Piscator. (t) "non avertisti", Grotius.