Albert Barnes Commentary Psalms 17:8

"Keep me as the apple of the eye; Hide me under the shadow of thy wings," — Psalms 17:8 (ASV)

Keep me as the apple of the eye - Preserve me; guard me; defend me, as one defends what is most precious and valuable. In the original, there is a remarkable strength of expression and, at the same time, a remarkable confusion of gender in the language. The literal translation would be, “Keep me as the little man - the daughter of the eye.” The word “apple” applied to the eye means the pupil, the little aperture in the middle of the eye, through which the rays of light pass to form an image on the retina (Johnson, Webster); though why it is called the “apple” of the eye the lexicographers fail to tell us.

The Hebrew word - אישׁון 'ı̂yshôn - properly means “a little man,” and is given to the apple or pupil of the eye, “in which, as in a mirror, a person sees his own image reflected in miniature.” This comparison is found in several languages. The word occurs in the Old Testament only in Deuteronomy 32:10; Psalms 17:8; and Proverbs 7:2, where it is rendered “apple;” in Proverbs 7:9, where it is rendered “black;” and in Proverbs 20:20, where it is rendered “obscure.” The other expression in the Hebrew - “the daughter of the eye” - is derived from a usage of the Hebrew word “daughter,” denoting what is dependent on or connected with (Gesenius, Lexicon), as the expression “daughters of a city” denotes the small towns or villages lying around a city and dependent on its jurisdiction (Numbers 21:25; Numbers 21:32; Numbers 32:42; Joshua 17:11).

So the expression daughters of song (Ecclesiastes 12:4). The idea here is that the little image is the child of the eye, that it has its birth or origin there. The prayer of the psalmist here is that God would guard him, as one guards their sight—an object so dear and valuable to them.

Hide me under the shadow of your wings - Another image denoting substantially the same thing. This is taken from the care shown by birds in protecting their young by gathering them under their wings. . Both of the comparisons used here are found in Deuteronomy 32:10-12, and it is probable that the psalmist had that passage in mind: He instructed him, he kept him as the apple of his eye; as an eagle stirreth up her nest, fluttereth over her young, spreadeth abroad her wings, taketh them, beareth them on her wings; so the Lord alone did lead him. (Psalms 57:1; Psalms 61:4; Psalms 63:7; Psalms 91:1; Psalms 91:4).