In verse 4 the personal pronoun changes from he to you. David is not speaking about the shepherd but speaking to the shepherd. In the dark valley, He is not before us but beside us, leading the way and calming our fears. The “vale of deep darkness” represents any difficult experience of life that makes us afraid, and that includes death. Sheep lack good vision and are easily frightened in new circumstances, especially where it’s dark; and the presence of the shepherd calms them.

The rod was a heavy cudgel with which the shepherd could stun or kill an attacking beast, and the staff was the shepherd’s crook, which he used to assist the individual sheep. At evening, he would have the sheep pass under the crook one by one so he could count them and examine them (Lev. 27:32). It gave the flock peace knowing that the shepherd was there and was equipped for any emergency. He is “Immanuel … God with us” (Matt. 1:23).

Jesus is not a hireling who runs away at the sight of danger; he is a true Shepherd who lay down his life for his sheep (John 10:11–15). God’s sheep have “peace with God” (Rom. 5:1) and may enjoy “the peace of God” (Phil. 4:4–7) as they trust Him. Through life, as we follow the Shepherd, we will have many and varied experiences, some of which will be very trying, but none of them can take the Lord by surprise. We may trust Him and have peace. The closer we are to our Shepherd, the safer we are and the more His peace will fill our hearts. (See Isa. 40:9–11; 43:1–3; Rev. 1:17–18.)
-Wiersbe

Psalm 23:1–6 (MEV)

1 The Lord is my shepherd; I shall not want.

2 He makes me lie down in green pastures; He leads me beside still waters.

3 He restores my soul; He leads me in paths of righteousness for His name’s sake.

4 Even though I walk through the valley of the shadow of death, I will fear no evil; for You are with me; Your rod and Your staff, they comfort me.

5 You prepare a table before me in the presence of my enemies; You anoint my head with oil; my cup runs over.

6 Surely goodness and mercy shall follow me all the days of my life, and I will dwell in the house of the Lord forever.