The Christian life must be one of balance. In this particular verse of Psalm 119, we see that balance exemplified between heart and will; between the weight of our desires and emotions versus our duties as children of a King.
This protects us from sentimentalism and legalism. in other words, there is the head aspect of Christianity and the heart aspect. As John Flavel says, the distance between the head and the heart is great, but the distance between the heart and action is short. Psalm 119:10 gives us fuel for prayer to shorten that distance between the head, the heart, and the life.
With all my heart I have sought You;
Do not let me wander from Your commandments.