“I shall not want” is the theme of Ps. 23. I shall not lack for: rest and refreshment (v. 2), restoration and righteousness (v. 3), protection in trouble (v. 4), provision in the wilderness (v. 5), and a home to go to at the end of the days (v. 6).

More is implied than is expressed, not only, I shall not want, but, I shall be supplied, in my earthly pilgrimage, with all that I need; and, if I have not everything I desire, I may conclude it is either not fit for me or not good for me or I shall have it in due time.
– Adapted from Matthew Henry

The position of Psalm 23 is worthy of notice. It follows the twenty-second, which is peculiarly the Psalm of the Cross. There are no green pastures, no still waters without a God-forsaken, crucified Messiah. It is only after we have read, “My God, my God, why have You forsaken me?” that we come to “The Lord is my Shepherd.” We must by experience know our need of Jesus’ shed blood, and see the sword awakened against the Shepherd, before we shall be able truly to know the sweetness of our good Shepherd’s care.
– Adapted from Charles Spurgeon