He guards your heart and mind with peace
"Do not be anxious about anything, but in every situation, by prayer and petition, with thanksgiving, present your requests to God. And the peace of God, which transcends all understanding, will guard your hearts and your minds in Christ Jesus." (Phil. 4:6-7 NIV)
Many times in Scripture we are commanded to not be anxious about anything. Why would God ever command us to do anything that we could not control?
God enables you to do it!
I am also reminded of other promises such as "when we are weak, he is strong" (2nd Cor. 12:10), and his strength is made perfect in our weakness" (2nd Cor. 12:9), and even "I can do all things through Christ Jesus which strengthens me" (Phil. 4:13), In other words, God sends his help and strength to enable you to accomplish what he commands you to do!
This promise comes with instructions!
And, as many times you see in the Word of God, instructions are included along with the commands and promises. And, that is true here with this command to not be anxious about anything. "By prayer (speak to God about it) and petition (ask God for help about it) with thanksgiving (Thank God for the answer for it) present your requests to God (anything and everything about it, put in the form of direct requests to God about it). And, with this promise, God tells you what will happen if you follow and do the simple instructions in the verse, "And the peace of God, which transcends all understanding, will guard your hearts and your minds in Christ Jesus."
Fear is not from God!
Finally, remember that anxiety is fear and fear is not from God! (2 Tim. 1:7), It is an attack against you from the devil. But, God promises to "guard your heart and mind in Christ Jesus!" The battle is fought and won in your mind and it's wonderful to know that He has you covered!