Adam Clarke's Commentary on the Bible

Verse 18 (John 14:18)

I will not leave you comfortless - Literally, orphans. The original word ορφανος , is by some derived from ορφνος , obscure, dark, because, says Mintert, an orphan (one deprived of father and mother) is little esteemed, neglected, and is obliged to wander about in obscurity and darkness. Others derive it from the Hebrew חרף charaph , to strip or make bare, despoil, because such a child is destitute of comfort, direction, and support, and is a prey to misery and disease, to sin and to death.

The disciples of a particular teacher among the Hebrews called him father; his scholars were called his children, and, on his death, were considered as orphans. Christ calls his disciples children, beloved children, John 13:33 ; and, now that he is about to be removed from them by death, he assures them that they shall not be left fatherless, or without a teacher; for in a little time he should come again, (rise from the dead), and, after his ascension, they should be made partakers of that Spirit which would be their comforter, advocate, teacher, and guide for ever.

- Adam Clarke's Commentary on the Bible