John Trapp on Psalms 17:8

Verſ. 8. Keep me as the apple of the eye] Heb. As the black of the apple of the eye, two words to the ſame ſenſe, for more vehemency. q. d. Serva me ſtudioſiſſimè. The apple of the eye, that little man in the eye (as the Hebrew word importeth, the girl, [non-Latin text not transcribed] Huc pertinet locus Cicer. a De nat. deor. as the Greeks for like cauſe call it) is the tendereſt piece of the tendereſt part, the eye; which is kept moſt diligently, and ſtrongly guarded by Nature with tunicles. David therefore fitly prayeth to be ſo kept.

Hide me under the ſhadow of thy wings] Another excellent ſimilitude taken from Fowls, which either cover their Young with their wings from the ſcorching heat of the Sun beams, as doth the Eagle; or keep them thereby from the cold, or from the Kite, as Hens do. Gods love to, and care of his poor people is hereby ſhadowed out; as it was likewiſe by the out-ſpread wings of the Cherubins in the Sanctuary. See Ruth 2.12. Deut. 32.10. Zach. 2.8. Pſal. 36.8. & 57.2. Matth. 23.37.