Adam Clarke on Philippians 4:7

And the peace of God - That harmonizing of all passions and appetites which is produced by the Holy Spirit, and arises from a sense of pardon and the favor of God;

Shall keep your hearts - Φρουρησει· Shall keep them as in a strong place or castle. Your hearts - the seat of all your affections and passions, and minds - your understanding, judgment, and conscience through Christ Jesus; by whom ye were brought into this state of favor, through whom ye are preserved in it, and in whom ye possess it; for Christ keeps that heart in peace in which he dwells and rules. This peace passeth all understanding; it is of a very different nature from all that can arise from human occurrences; it is a peace which Christ has purchased, and which God dispenses; it is felt by all the truly godly, but can be explained by none; it is communion with the Father, and his Son Jesus Christ, by the power and influence of the Holy Ghost.