Psalm 23 is the sheep speaking about the Shepherd; John 10 is the Shepherd speaking about His sheep. In the former, although the writer was inspired by the Holy Spirit, David's experience of the Shepherd must necessarily have been limited. In the later the Good Shepherd knows all about His sheep perfectly, knows what poor wandering things we are, and in spite of it speaks of our not perishing, and having eternal life! How wonderful! What ample provision He has made for His own!
But there are two negatives in Psalm 23 lying like two precious glittering gems amid all the positive blessings that David enumerates:
shall not want" (v. 1);
"I will fear no evil" (v. 4).
If I do not want in the present, and do not fear for the future, then surely I am in a happy position.
David himself had been a shepherd, and as a king he was called to shepherd Jehovah's people; and he knew something of what it meant. If he could say the Lord is my Shepherd, "I shall not want" was a necessary deduction.
And the careful observer of the two scriptures will be able to trace all the blessings that the Good Shepherd tells us about in John 10, in Psalm 23, perhaps dimly and obscurely, but still there. Not, of course, in all the full light and relationship of Christianity, but still there in a Jewish mold. All this is deeply interesting and instructive and comforting. We can read Psalm 23 in the light of John 10.