casting all of your anxieties on him, because he cares for you -1 John 5:7The word casting means to throw upon; cast upon. The meaning conveys that there is an action on our part, we must cast upon Jesus our anxieties. It means we must be intentional at this. The carnal mind, the fleshly member, is against the Spirit, against trusting in God, it will fill your mind with anxieties, cares and worries so cast them upon Jesus.
be vigilant, be alert your adversary the devil walks around like a roaring lion seeing any to devour- 1 Peter 5:8
The verse about casting your anxieties is sandwich between humbling yourself under the mighty hand of God, and this verse. I take that in context to mean the devil uses anxiety against us. Much like unhealthy fear where the devil works, anxiety clouds the mind so you do not have peace. Jesus mentions anxiety, cares of this world, as a thorn that attempts to choke out our growth (Matthew 13:22; Luke 8:14; Mark 4:19).
... because he cares for you
Jesus wants us to cast our anxieties on him because he cares for us. He doesn't want us to be anxious about the cares of this world. To cast these cares on Jesus we must be intentional. Set your mind on it, and experience his peace. The peace might not last long so do it again, and again, and again... The burdens will be lifted, most likely not all at once so keep throwing it on him. You will find yourself delighting in the Lord, that he cares for you, as you cast the cares of this world on his shoulders, experiencing the lifting of them from yours. Such is a better place to be than burdened down with the cares of this world.
