Matthew Henry Commentary Genesis 15:1

"After these things the word of Jehovah came unto Abram in a vision, saying, Fear not, Abram: I am thy shield, [and] thy exceeding great reward." — Genesis 15:1 (ASV)

God assured Abram of safety and happiness: that he would forever be safe. I am thy shield; or, I am a shield to you, present with you, actually caring for you.

The consideration that God himself is and will be a shield to his people—a shield to secure them from all evils, a shield ready for them, and a shield around them—should silence all perplexing, tormenting fears.