Rejoice in the Lord always; again I will say, rejoice. 5 Let your reasonableness be known to everyone. The Lord is at hand; 6 do not be anxious about anything, but in everything by prayer and supplication with thanksgiving let your requests be made known to God. 7 And the peace of God, which surpasses all understanding, will guard your hearts and your minds in Christ Jesus.
The practice of guarding your heart and mind is not to be entered upon haphazardly. This passage contains several commands of the Lord which His people are to follow, and which have a promise connected to them. The commands are: Rejoice in the Lord always. Be reasonable/humble/circumspect in the way you walk because the Lord is near. Do not be anxious/worried/fretful about anything (notice the Lord's great kindness here in giving us something productive to do, rather than merely telling us what not to do); but pray about everything with supplication and thanksgiving (God is encouraging us to ask Him for what we perceive as good gifts). The promise is that God's peace (which is so far beyond our feeble ability to reason it out) will guard our hearts and minds. (!!!!!!!)
How kind and good our Lord Jesus is to encourage our hearts with these words. How mercifully and tenderly He cares for His people, growing and guarding us in His ways and in His paths. May we become more like Him every day.