Thomas Manton on Psalm 119:32

    I will run in the way of your commandments
        when you enlarge my heart!
(Psalm 119:32 ESV)

The general enlargement is at regeneration or conversion to God. When we are freed from the bonds of natural slavery, and the curse of the law, and the power of sin, to serve God cheerfully, then is our heart said to be enlarged. This is spoken of in scripture: John viii. 36, If the son shall make you free, ye shall be free indeed.' There are two things notable in that scripture--that this is freedom indeed, and that we have it by the Son. That this the truest liberty, then are we free indeed.

   1. You may look upon this enlargement as the effect of wisdom and knowledge; and so Solomon is said to have a large heart: 1 Kings iv. 29, And God gave Solomon wisdom and understanding exceeding much, and largeness of heart even as the sand that is on the sea shore.'

   2. You may look upon it as the effect of faith, which wideneth the capacities of our souls, and doth cause us more to open towards God, that we may take in his grace; it doth enlarge our desires and expectations: Ps. lxxxi. 10, Open thy mouth wide, and I will fill it.'

   3. We may look upon it as an effect of comfort and joy, through the assurance of God's love; for that enlargeth the heart, but sorrow straitens it, and puts it in bonds.

   4. We may look upon it as a fruit of love. For thus the apostle doth express his love to the Corinthians, 2 Cor. vi. 11, O ye Corinthians, our mouth is open unto you, our heart is enlarged.'

Manton, Thomas (2011-11-08). The ULTIMATE Collected Works of 19 Books (With Active Table of Contents) (Kindle Locations 69991-69993). Kindle Edition.