William Burkitt on Matthew 12:35

Observe here, A double treasure discovered in the heart of man.

1. An evil treasure of sin and corruption, both natural and acquired, from whence proceed evil things. Now this is called a treasure, not for the preciousness of it, but for the abundance of it; a little doth not make a treasure: and also for the continuance of the life, yet doth the heart continue full; nature may be drawn low in this life, by sanctifying grace, but it never can be drawn dry.

2. Here is a good treasure of grace discovered in a sanctified and renewed man; which is the source and spring from whence all gracious actions do proceed and flow. For as the heart of man by nature is the fountain from whence all sin springs, so the heart renewed by grace is the source and spring from whence all gracious actions do proceed and flow.