Albert Barnes Commentary Job 3:16

"Or as a hidden untimely birth I had not been, As infants that never saw light." — Job 3:16 (ASV)

Or as a hidden untimely birth - As an abortion which is hidden or concealed; that is, which is soon removed from sight. So the Psalmist (Psalms 58:8):

As a snail which melts, let them dissolve;
As the untimely birth of a woman, that they may not see the sun.

Septuagint ἔκτρωμα ektrōma — the same word that is used by Paul in 1 Corinthians 15:8, with reference to himself; see the notes on that passage.

I had not been - I should have perished; I should not have been a man, as I now am, subject to calamity. The meaning is, that he would have been taken away and concealed, as such an untimely birth is, and that he would never have been numbered among the living and the suffering.

As infants who never saw light - Job expresses here no opinion of their future condition, or on the question whether such infants had immortal souls. He is simply saying that his lot would have been as theirs was, and that he would have been saved from the sorrows which he now experienced.