"Cast your cares on the Lord and he will sustain you." Psalm 55:22
Care, even though exercised upon legitimate objects, if carried to excess, has in it the nature of sin. The precept to avoid anxious care is earnestly inculcated by our Savior, again and again; it is reiterated by the apostles; and it is one which cannot be neglected without involving transgression: for the very essence of anxious care is the imagining that we are wiser than God, and the thrusting ourselves into His place to do for Him that which He has undertaken to do for us. We attempt to think that which we fancy He will forget; we work to take upon ourselves our weary burden, as if He were unable or unwilling to take it for us. Now this disobedience to His plain precept, this unbelief in His Word, this presumption in intruding upon His providence, is all sinful. Yet more than this, anxious care often leads to acts of sin. He who cannot calmly leave his affairs in God's hand, but will carry his own burden, is very likely to be tempted to use wrong meants to help himself. This sin leads to a forsaking of God as our advisor, and resorting instead to human wisdom. This is going to the "broken cistern" instead of to the "fountain;" a sin which was laid against Israel of old. Anxiety makes us doubt God's loving-kindness, and thus our love to Him grows cold; we feel mistrust, and thus grive the Spirit of God, so that our prayers become hindered, our consistent example marred, and our life one of self-seeking. Thus want of confidence in God leads us to wander far from Him; but if through simple faith in His promise, we cast each care as it comes upon Him, and are "not anxious about anything" because He undertakes to care for us, it will keep us close to Him, and strengthen us against much temptation. "You will keep in perfect peace him whose mind is steadfast, because he trusts in You."
After reading over this a few times, I was struck with the fact that we are pretty much instructed by the Lord to "keep in perfect peace" as believers, because He has given us peace as a Fruit of the Spirit and He wants us to cast all of our cares on Him.
I know this is a basic precept-to trust in Him, but sometimes we need a reminder, a "light bulb" moment, to step back and look at how we are dealing with situations in our lives.