“plans of the heart.” This is one of the Proverbs that is not universally applicable, but is applicable to people who living a godly lifestyle, or it can be considered an “ideal” proverb, setting forth the ideal situation, not the situation that always happens here on earth. There are a number of proverbs like this in Proverbs (cp. Prov. 11:31; 13:25; 15:6; 16:3, 7, 10; 18:3; 20:8; 21:1; 22:6).
The Hebrew word “plans” is maarak (#04633 מַעֲרָךְ), and it refers to an arrangement, plan, preparation. In this context, it conveys placing things in careful order or setting them next to each other for comparison, as we do when making plans. The “plans of the heart” are a person’s internal thoughts and intentions, which are devised according to the person’s will and desires.
The plans “of the heart” that people make eventually come out in what they say (Matt. 12:34; 15:18; Mark 7:14-23; Luke 6:45), but godly people want and intend to say things that are godly and agree with the written Word and God’s heart for mankind. Given that, the “answer of the tongue” they are seeking ultimately comes from God. This Proverb does not imply that a person’s response is outside of the speakers free will as if what the person said was somehow controlled by God; rather it is saying that a proper answer can only be found in the wisdom that God gives. The proverb does not discourage human planning but cautions that a person should not be self-reliant or overly-confident in their own understanding and abilities but plan and speak in a way that reflects the wisdom of God (cp. Prov. 3:5-7). Doing that requires seeking wisdom and making the effort to be godly in thought and action. This proverb invites the willing reader to actively seek God in how he might devise godly plans and how to speak in such a way that those plans are articulated in a loving and godly way so they will eventually come to fruition and be put into action.
“of the heart.” Biblically, the “heart” can refer to the mind, the thinking, of the core of one’s inner life, and much more. Here it means the plans a person forms in his mind or the depths of his mind, or in the core of his inner self. [For more on “heart,” see commentary on Prov. 16:21, “sense”].
“tongue.” The use of “tongue” is the figure of speech synecdoche of the part, putting the part for the whole, where the part, the tongue, is put for the whole, i.e., the whole person. The answer the person gives is from Yahweh because wisdom and godliness are from Yahweh.