4 Though I walk through the valley of the shadow of death, The world is the dimension controlled by the god of this world — Satan, the selfish spirit in man that lusts, lies, kills, steals, rages, covets, etc. Death is a daily event in the news of the world. Death stalks all men. The valley of the shadow of death is the world and the institutions of the world, including Babylon's beast with horns like a lamb, that imitates Christianity; which offers a covenant with Hell that shall be annulled and ends in death.
The shadow of death is darkness; all men sit in darkness and walk in darkness until their hearts have been purged from the evil that defiles them. From the Word of the Lord within: "All sin is darkness. I have come as a light to the world so that whoever believes in me shall not abide in darkness. I am the light of the world; he who follows me shall not walk in darkness but shall have the light of life. The whole world lies in wickedness; the wickedness knows no shame. Darkness mocks the earth; darkness covers the earth."
I will fear no evil, for you are with me;. If one commits to seeking the Kingdom of God and His righteousness as their first priority in life, making it more important than food, clothing, or money, then you will have the protection of God. You will have nothing to fear, because the shepherd (Christ) watches over you. The shepherd controls the whole universe by the power of his word, and he makes all things work together for good to those who love him (obey him) and are called to his purpose.
your rod and your staff they comfort me. The rod is used to discipline a sheep, the staff to drag him back into line. When a man is seeking the Lord, even the pain of discipline can be a comfort. Just knowing that the Lord is still dealing with us, and has not abandoned us, even if it is a painful reminder, is reassurance and comfort. The full soul loathes a honeycomb; but to the hungry soul every bitter thing is sweet.