Psalm 23 is probably the best known and widely memorized of all the psalms. It gives peace, comfort, spiritual strength, encouragement, and happiness to all those who trust in the Lord. The analogy of the Shepherd and sheep is found throughout the whole Bible. It points to the kind, compassionate, gentle, and good shepherd, the Lord Jesus Christ. Jesus often referred to Himself as a shepherd, and many New Testament writers and Old Testament prophets spoke of Jesus as the Good Shepherd (John 10:11-19; 26-28; Hebrews 13:20; 1 Peter 2:25; 5:4; Isaiah 40:11; 49:9-10; Jeremiah 31:10-12). He came to seek and to save the lost sheep on whom He had compassion when He saw they were without a worthy shepherd (Luke 15:4-7; Isaiah 53:6). Unlike the selfish shepherds of Israel (Ezekiel 34:2-6), the Lord is the good and faithful Shepherd who lovingly cares, guides, protects, and comforts His sheep. He searches for those that are lost, feeds them, gives them rest, and binds their wounds (Ezekiel 34:11-16). The Lord always held shepherds in high regard, such as the patriarchs, Moses, David, Amos, and the list goes on. David's experience as a shepherd and his lifetime of trusting in God helped him to write this psalm with great insight.
There is a small but significant word; the Lord is called "My" shepherd. What gives us the right to consider ourselves His sheep? The preceding psalm provides the basis; it was the atoning sacrifice of Jesus Christ, the Good Shepherd, who gave His life for "the sheep" (Jesus died for the whole world), but those who are His sheep are those known by Him (born of the will of God) and those who know Him (John 10:11, 14), because they have "recieved Him", since they "believe in His name" (John 1:12-13).
Consider all the good things enjoyed by the sheep of the Lord: He provides physical sustenance (food and water; 23:1-2) and every temporal need, just as would a typical, gracious and hospitable middle-eastern host (23:5). He gives rest in "green pastures". Such pastures are scarce in the Holy Land, so the shepherd would have to lead the flock from pasture to pasture. The sheep, then, are actively involved in trustfully following the Shepherd, so they might continually find this peaceful rest with Him.
The Good Shepherd, also provides for the spiritual needs of His sheep. By following and obeying Jesus, we are restored to communion with God (23:3). What is the reason the Shepherd leads us in the paths of righteousness? For His Name's sake. It is purely because of His grace, and we have done nothing to deserve it. When we live righteously, it brings honour and glory to the Name of God. The sheep's conduct reflects on the shepherd.
When the sheep travel from one restful pasture to another, they must often pass through narrow valleys with rocky cliffs and caves on either side. The shepherd's guidance and presence provides the sheep with safety from harm (Psalm 78:52-54), so the trustful follower need not fear. The loving shepherd must often use his rod to keep his sheep from wandering into dangerous places where bears or lions may be hiding, and although the rod may hurt sometimes, it is actually a good thing which brings comfort. While in the valley, the "shadow of death" might be seen (23:4), but a shadow does not harm, nor does it lead to death, just as the shadow of a lion does not kill. Wherever there is a shadow, there must also be light. Before the shadow of death, there is the Light of Jesus Christ (27:1; John 8:12), and "He turns the shadow of death into morning" (Amos 5:8). His death abolished death and His resurrection brought the light of life to those who follow Him (2 Timothy 1:10). "Goodness and mercy" not only "follows" but "pursues" the Lord's sheep and they can have the confidence that they will have communion with the Lord forever (23:6).
Psalm 24 is a majestic hymn, likely sung responsively by two choirs — one questioning and the other answering. It was possibly written at the time David successfully and joyously brought the Ark up to Jerusalem (2 Samuel 6:12ff). They sung of God's glory, dominion, and sovereignty over the earth and all His creation (cf. Colosians 1:15-17). They answered that only those who seek Him with a pure heart are worthy to stand before Him. As the procession approached the city of Jerusalem with the Ark, representing the presence of God, they spoke to the gates and doors to open wide to gladly receive their glorious and mighty King.
Psalm 25 is a psalm of the penitant in suplication for God's forgiveness of sin and deliverance from enemy threats. Interestingly, it is an acrostic poem, using the successive letters of the Hebrew alphabet as a framework, and for this reason the thoughts do not flow together as smoothly as in most other psalms. David's trust in the Lord was so great, because he waited in faith on the Lord "all the day". He prayed without ceasing, for he committed all his ways to the Lord. He prayed: "show me", "teach me", and "lead me", so that he would always keep God's covenant, live righteously, and fear the Lord.