en_tn_condensed/psa/071/003.md

Be to me a rock for refuge

The psalmist requests that Yahweh make him as safe as he would be if he were hiding in a large rock or cliff where his enemies could not find him.

you are my rock and my fortress

The psalmist believes that Yahweh will protect him and make him as safe as if he were hiding on top of a large mountain or inside a man-made fortress.