Physiologically, the heart is an organ in the body, and in the Bible it is also used in a number of metaphors. The NT uses the Greek term kardia similarly to the OT Hebrew terms leb and lebab and in some cases depends on OT usage.

Mind and Emotions

Metaphorically, the heart refers to the mind, the will, the seat of emotions, or even the whole person. It also refers to the center of something or its inner part. These metaphors come from the heart’s importance and location.

Mind. The heart refers to the mind, but not the brain, and in these cases does not involve human physiology. It is a metaphor, and while the neurophysiology of the heart may be interesting in its own right, it has no bearing on this use of language. We also should not confuse some modern English idioms or distinctions as being related to the biblical viewpoint. The Bible does not make a distinction between “head knowledge” and “heart knowledge,” nor does it employ language making the “heart” good or superior and the “head/mind” bad, inferior, or merely intellectual. It does not prize the emotional over the thoughtful; it has a more integrated viewpoint.

Deuteronomy 6:5 issues the command to love God with all one’s heart, soul, and strength. When the command is repeated in the Gospels, it occurs in three variations (Matt. 22:37; Mark 12:30; Luke 10:27). Common to all three is the addition of the word “mind.” The Gospel writers want to be sure that the audience hears Jesus adding “mind,” but this addition is based on the fact that the meaning of the Hebrew word for “heart” includes the mind.

The mental activities of the metaphorical heart are abundant. The heart is where a person thinks (Gen. 6:5; Deut. 7:17; 1 Chron. 29:18; Rev. 18:7), where a person comprehends and has understanding (1 Kings 3:9; Job 17:4; Ps. 49:3; Prov. 14:13; Matt. 13:15). The heart makes plans and has intentions (Gen. 6:5; 8:21; Prov. 20:5; 1 Chron. 29:18; Jer. 23:20). One believes with the heart (Luke 24:25; Acts 8:37; Rom. 10:9). The heart is the site of wisdom, discernment, and skill (Exod. 35:34; 36:2; 1 Kings 3:9; 10:24). The heart is the place of memory (Deut. 4:9; Ps. 119:11). The heart plays the role of conscience (2 Sam. 24:10; 1 John 3:20–21).

It is often worth the effort to substitute “mind” for “heart” when reading the Bible in order to grasp the mental dimension. For example, after telling the Israelites to love God with all their heart, Moses says, “These commandments that I give you today are to be upon your hearts” (Deut. 6:6). Reading it instead as “be on your mind” changes our perspective, and in this case the idiom “on your mind” is clearer and more accurate. The following verses instruct parents to talk to their children throughout the day about God’s words. In order for parents to do this, God’s requirements and deeds need to be constantly on their minds, out of their love for him. Similarly, love for God and loyalty are expressed by meditation on and determination to obey his law (Ps. 119:11, 112). The law is not merely a list of rules; it is also a repository of a worldview in which the Lord is the only God. To live consistently with this truth requires careful, reflective thought.

Emotions and attitude. The heart, as the seat of emotion, is associated with a number of feelings and sentiments, such as gladness (Exod. 4:14; Acts 2:26), hatred (Lev. 19:17), pride (Deut. 8:14), resentment (Deut. 15:10), dread (Deut. 28:67), sympathy (Judg. 5:9), love (Judg. 16:15), sadness (1 Sam. 1:8; John 16:6), and jealousy and ambition (James 3:14). The heart is also the frame of reference for attitudes such as willingness, courage, and desire.

Idioms

The word “heart” also appears in several idioms.

Hardness of heart. A hard heart is obstinate or averse (Mark 3:5), while a tender heart is humble (2 Kings 22:19). In the book of Exodus the translations typically say that God or Pharaoh hardened Pharaoh’s/his heart. These passages in Exodus use not the Hebrew words for hardness but rather those for being heavy or for strengthening. The neutral sense of strengthening the heart takes on nuances in context for being bold or obstinate. Pharaoh was strengthened in his opposition to God, and this obstinacy fits the idiom of having a hard heart.

Uncircumcised/circumcised heart. An uncircumcised heart is a metaphor for an obstinate and rebellious heart, while a circumcised heart is linked to being humble and faithful (Lev. 26:41; Deut. 30:6; Jer. 4:4; Acts 7:51). Perhaps the metaphor is based on the role of circumcision in the covenant.

“A man after his [God’s] own heart” (1 Sam. 13:14). This description of David may mean either “according to his [God’s] choice” (cf. 2 Sam. 7:21), stressing God’s choice over the people’s choice, or it may mean “in accordance with his [God’s] desire” (1 Sam. 14:7; 1 Kings 15:3), referring to how David showed conformity with God’s agenda.

All the heart. The phrase “with all [one’s] heart” in some cases means “wholeheartedly” or “single-mindedly,” which emphasizes unity of purpose and focus. In other cases it seems to mean, more broadly, “with all of one’s thinking or perspective” and implies the work of adjusting our worldview away from common cultural assumptions and toward God’s teaching.

Say in one’s heart. This expression denotes talking to oneself (i.e., thinking) rather than out loud or indicates reflection or deliberation. There are several warnings not to lie to oneself—that is, not to deliberate, believe, and act on the stated false premise.

Take [a matter] to heart. To take something to heart is to take it very seriously or to give it high priority.