'Keep and guard you heart with all vigilance and above all that you guard, for out of it flow the springs of life' (Amp).
Like all the Puritan writers his work is dense and doesn't lend itself to easy summarisation. However he opens his short book which can be found here on the internet with these words:
The heart of man is his worst part before it is regenerated, and the best afterward; it is the seat of principles, and the fountain of actions. The eye of God is, and the eye of the Christian ought to be principally fixed upon it.
The greatest difficulty in conversion, is to win the heart to God; and the greatest difficulty after conversion, is to keep the heart with God. Here lies the very force and stress of religion; here is that which makes the way to life a narrow way, and the gate of heaven a strait gate.
