A cast sheep is a sheep that has fallen on its back, legs straight up in the air. It can't rise on its own and will die within a few hours if the Shepherd doesn't find it in time.
Phillip Keller, author of "A Shepherd Looks At Psalm 23" says, "a sheep becomes cast when it rolls on its side to relax after lying down in a hollow or depression in the ground. It is during this time gravity in the body shifts and when it turns to get back on its feet, it discovers its feet can no longer touch the ground. It begins to panic and paw frantically. As it lies there struggling, gases begin to build in the rumen. The gases will cut off blood circulation to the extremities of the body, especially the legs."
Notice, the sheep became cast when it decided to relax on hollow grown. The word hollow refers to a hole or empty space. It can also refer to something that is valueless, worthless, futile or fruitless.
As Christians we often find ourselves resting or relaxing in hollow places. Places that are futile, worthless, fruitless and valueless. Hollow places can be time spent in bad relationships, living with bad habits, seeking or pursing mammon/money before God. Unfortunately, when we try to get up and move on with our lives, we find ourselves crippled with troubling emotions, empty pockets, ruined relationships or bad health. We discover we are unable to walk like we used to or we discover we can't correct the situation as easily as we want to, so we panic and that makes matters worse.
Thank God the Good Shepherd is diligently looking for cast sheep. Don Baker, author of "The Way of the Shepherd", says, when the shepherd finds a cast sheep he begins to massage its limbs and body. The gases are dispelled, the blood begins to flow and within time, the sheep is back on its feet again, running off to join the rest of the flock.
Notice, the Shepherd doesn't scold the sheep for being cast but lovingly begins to help it and take care of it! And so it is with us, the sheep of God's pasture. We can rejoice for we have a shepherd who loves us and desires to take care of us even when we fail and become cast down!
Take a look at what David said to the sheep of God's pasture.
Psalm 100:3 Know ye that the LORD he is God: it is he that hath made us, and not we ourselves; we are his people, and the sheep of his pasture.
Psalm 100:4 Enter into his gates with thanksgiving, and into his courts with praise: be thankful unto him, and bless his name.
Psalm 100:5 For the LORD is good; his mercy is everlasting; and his truth endureth to all generations.
Yes, let's be thankful that our Shepherd is good and full of everlasting mercy. His mercy, forgiveness, and willingness to help us never ends and that's the truth for all of us!