In the ancient world, they didn’t have supports for grape vines. Grapevines ran along the ground. Which meant the farmer had to lift up branches with small stones, rocks, or other branches, to keep the grapes from touching the ground. More than this, every year, the farmer clipped off the branches that did not bear fruit – and he pruned the branches that did. Pruning comes from the root, “to lift up.” On a surface reading it would mean God cuts off the bad stuff.
But what if it means “to lift up?” Imagine God, the gardener, walking up and down these rows. He sees a branch struggling, that is touching the ground – if grapes touch the ground, they turn sour and they are not good for anything (Isaiah uses this imagery about grapes that drag along on the ground – they turn sour and they rot). What does He do? Lift them up.
And to help the branches dragging along the ground because of the weight of their fruit, he cuts off the ones that don’t bear fruit – and lifts up those that struggle. Maybe this should be of great encouragement to us.