Faith is “the resting of the heart on God.”
The above statement was made by the puritan William Ames (1576 – 1633) in his classic work The Marrow of Theology. Ames’ beautiful definition of faith teaches us exactly what true faith is and what it should produce. Ames defines faith more as an action that prescribes not only our intellect but also our emotions, and ultimately our trust.
Faith is often seen as something that is if not solely, at least mostly intellectual. Faith is often defined as “belief.” You must “believe God,” if so you have “faith.” What Ames draws out is that faith is more than just intellectual belief. True faith is also trust; it is the mixture and perfection of belief and trust. Faith is, therefore, belief and trust in God. We must not forget that faith besides being intellectual it is also personal and emotional. When we have faith in God we do not simply have faith in a concept or power, but a person. We must not forget that God is a person (to be more exact three persons in one essence), and therefore; when we say that we have faith in God we must not forget that we are placing our faith in the personhood of God.
In the words of Ames, true faith is resting our hearts on the personhood of God. This is faith that rests on the Father for provision, grace, guidance, wisdom, and love. This kind faith rests on the Son for salvation, redemption, compassion, and purpose. This kind of faith rests on the Holy Spirit for illumination of the Word, power, renewal, and strength.
As imperfect people, we often look to many false sources for our needs. We look to other people for wisdom, love, guidance, etc. We try to find purpose in our endeavors, job, family, etc. We seek to gain power through money or position. While none of these things are bad in themselves, when taken in the place of God they become idols. Which is why we must remind ourselves what true faith requires. True faith looks to God and God alone as the only true source of all our needs. This is having a faith that rests on the heart of God.
 Beeke, Joel R.; Jones, Mark. A Puritan Theology: Doctrine for Life (Kindle Location 1934). Kindle Edition.