John Piper in Think: The Life of the Mind and the Love of God:
[O]ur thinking should be wholly engaged to do all it can to awaken and express the heartfelt fullness of treasuring God above all things.
What do the terms heart, soul, and mind refer to? What is plain from the Bible is that they overlap in meaning. Nevertheless, they do have different focuses. Concerning heart and mind, consider that the one other place in the four Gospels where the word mind (dianoia) occurs, other than in the command to love God, is Luke 1:51. There it is translated “thoughts,” and these thoughts are happening, surprisingly, in the “heart.” “He has scattered the proud in the thoughts (dianoia) of their hearts.” So mind and heart overlap. The heart has its thoughts and the mind has its “spirit” or, you might say, its “heart,” as Paul says in Ephesians 4:23: “Be renewed in the spirit of your minds.” Nevertheless, the mind and heart are not identical.
Concerning the meaning of the soul, consider that Jesus said, “Do not fear those who kill the body but cannot kill the soul. Rather fear him who can destroy both soul and body in hell” (Matt. 10:28). This implies that soul is the fullness of life or personhood apart from the body. The body can be killed and yet the soul still live. Therefore, the soul includes the heart and the mind, since Jesus says that though the body may perish, the soul is rescued, which would surely include the rescue of the heart and the mind as part of the soul.
What then shall we say about these terms? We may summarize like this: heart highlights the center of our volitional and emotional life without excluding thought (Luke 1:51). Soul highlights our human life as a whole (“man became a living creature,” Gen. 2:7), though sometimes distinguished from the body (Matt. 10:28). Mind highlights our thinking capacity. And when the term strength is added, as in Mark 12:30, it highlights the capacity to make vigorous efforts both bodily and mentally (Mark 5:4; Luke 21:36).