Shepherding in the ancient Near East did not work the way herding does now. The shepherd did not drive the flock forward from behind. He walked in front and the sheep followed his voice.
The difference matters. Being driven means pressure from behind, anxiety, obligation, the sense of being pushed toward something. Being led means someone has already walked the ground you are about to cross.
There is nowhere you are going today that He has not been. Not grief, not humiliation, not betrayal by people close to you, not the specific loneliness of being misunderstood. He has been on that road.
I shall lack nothing is not a promise of abundance. It is a statement about sufficiency in the presence of a competent guide.
You may lack many things you want. You will not lack what you need to get through today.