Matters of the mind or heart?

Matters of the heart and matters of faith go hand-in-hand. If one is present, the other will also be. When we take part in and engage God by faith, this is primarily an activity of our heart; of what we believe and trust to be true. 

This is in contrast to matters of the mind or understanding. We can clearly grasp something logically with our minds and even fully agree with it but not necessarily believe it in our hearts. To simply comprehend something does not mean we wholly and fully believe it, or "buy into it" as they say. When you do, that means you "put your money where your mouth is," or have "skin in the game" i.e. your beliefs require or cost you something because they result in action i.e. an investment of resources/time/energy.

Evidence that we fully believe something versus merely grasping it in our minds is action/obedience. When we truly believe something, we act on it. If we merely grasp or comprehend something -- even if we fully agree it is according to truth -- but do not take action, we do not truly believe it.

When presented with the truth, we can positively respond in two ways. We can agree it is true and we can believe it is true. When we agree, we are giving mental assent to something's truthfulness. When we believe it, we are acting on it and staking our resources/time/energy on its validity.

We cannot have the latter (faith) without the former (knowledge) but we can have the former without the latter.