Joshua is told to do something like this in Joshua 1:8
This Book of the Law shall not depart from your mouth, but you shall meditate on it day and night, so that you may be careful to do according to all that is written in it. For then you will make your way prosperous, and then you will have good success.
It's not supposed to depart from his mouth because that's what meditating on God's Word is, a mumbling, a telling, a speaking or groaning. Not simply some internal practice of processing but with it comes the idea of an utterance. It's the same idea at the beginning of Psalms.
1:2 But his delight is in the law of the Lord, and on this law he meditates day and night.
3b... in all that he does, he prospers.
It's the undertow of who you are, the mumblings throughout the day. Someone cuts in front of you, mumble... you don't get recognized at work, mumble... you have a hard day with the kids, mumble...
But whats coming out of your mouth?
I choose today to mumble on God's Word to see it come off my lips when life presses down. I know that can only happen if I practice meditating, mumbling in the peaceful quiet times.