This matter of shepherding God's flock for the main purpose and ultimate consummation of the eternal economy of God is even referred to in Song of Songs. In this book Christ shepherds His seeker and pursuer.
In Song of Songs 1:7a the seeker says, "Tell me, you whom my soul loves, Where do you pasture your flock [for satisfaction]?/Where do you make it lie down at noon [for rest]?"
The Shepherd responds to the seeker by saying, "Go forth on the footsteps of the flock,/And pasture your young goats /By the shepherds' tents" (1:8b). Under the Lord as the Chief Shepherd there are many other shepherds. The many shepherds pasture their young by their tents, that is, where they live.
Song of Songs 2:16 says, "My beloved is mine, and I am his;/He pastures his flock among the lilies [the seekers of Christ who live a life of trusting in God with a single heart]." The Lord is pasturing all His seekers as lilies, taking care of them, feeding them, and shepherding them that they may grow.
Song of Songs 6:3 says, "I am my beloved's, and my beloved is mine;/He pastures his flock among the lilies." To shepherd the believers is very crucial for their growth in life.
Without John 21, the Gospel of John does not have an adequate and complete ending.