The Lord is my light - He is to me the source of light. That is, He guides and leads me. Darkness is the emblem of distress, trouble, perplexity, and sorrow; light is the emblem of the opposite of these. God furnished him such light that these troubles disappeared, and his way was bright and happy.
And my salvation - That is, He saves or delivers me.
Whom shall I fear? - Compare Romans 8:31. If God is on our side, or is for us, we can have no apprehension of danger. He is abundantly able to protect us, and we may confidently trust in Him. No one needs any better security against the objects of fear or dread than the conviction that God is his friend.
The Lord is the strength of my life - The support of my life. Or, in other words, He keeps me alive. In itself life is feeble, and is easily crushed out by trouble and sorrow; but as long as God is its strength, there is nothing to fear.
Of whom shall I be afraid? - No one has power to take life away while He defends me. God is to those who put their trust in Him a stronghold or fortress, and they are safe.