Let's look at what these images are telling us.
When the psalmist describes God as a rock, he must have a really big rock in mind. He usually couples the word "rock" with "fortress" , "stronghold", or "refuge". A high rocky fortress would be nearly impregnable to enemies. So God's protection gives us both a place of safety where we can hide ourselves when weary, and a vantage point from which we may confidently attack the enemy.
That much is obvious.
Then there's the other Hebrew image of God as Rock-the rock that gave them water in the dessert. Psalms 78, 105, and 114 all reference this miracle. And St. Paul references the tradition, not explicitly stated in Exodus, that the miraculous, water-giving rock followed the chosen people in the dessert. He goes a step further, by saying "the rock who followed them was Christ." (1st Corinthians 10:4)
So our own meditations when reading about water from the rock will include Christ as the source of living water (salvation, grace, baptism).
Then there's Psalm 81, where the voice of God longs to feed his people with finest wheat and "honey from the rock". Convert from Judaism Roy Schoemann says that this verse describes God's wish to give his people the fullness of grace that comes with accepting Christ and His Church. And, obviously, it is an image of the Eucharist.
So much to think about when your daily prayer turns up a psalm that mentions a Rock. And here's one more, just to add a dash of typology to tickle your Catholic sensibilities: St. Peter, the rock on which Jesus built His church.
Stuff like this can make it hard to finish Morning or Evening Prayer. You just want to stay with one insight and leave the rest for another time. Which is okay, actually. If the Holy Spirit is giving you a gift, just take the time to play with it. We laity are not obliged to finish each day's morning of evening prayer. If we allow a crying baby or a phone call to prevent us from finishing, why not allow the prayer itself to do the same thing?
