Answer:
The “apple of the eye” is the pupil in your eye. It is the most sensitive part of the human body, and we all know what it feels like even when we get a speck of dust in our eye. We would do anything to protect our eye, and when it hurts our whole body responds.
So God’s love and care is to those who call Him their own. He protects us and cares for us in the same way we prize that most sensitive, precious part of our eye.
When something tries to harm us (especially those things with eternal consequences), God will react in kind to keep us and protect us.
Deuteronomy 32:10 He found him in a desert land, and in the waste howling wilderness; he led him about, he instructed him, he kept him as the apple of his eye.
Psalms 17:8 Keep me as the apple of the eye, hide me under the shadow of thy wings,
Proverbs 7:2 Keep my commandments, and live; and my law as the apple of thine eye.
Lamentations 2:18 Their heart cried unto the Lord, O wall of the daughter of Zion, let tears run down like a river day and night: give thyself no rest; let not the apple of thine eye cease.
Zechariah 2:8 For thus saith the LORD of hosts; After the glory hath he sent me unto the nations which spoiled you: for he that toucheth you toucheth the apple of his eye.