This mitzvah forbids a person from following the impulses of the heart or the temptations of the eyes when they lead away from the Torah. The Torah commands: “And you shall not stray after your hearts and after your eyes, after which you go astray” (Bamidbar 15:39).

Rambam explains that following the heart leads to heretical thought, while following the eyes leads to immoral action (Hilchos Avodas Kochavim 2:3). The mitzvah therefore addresses both belief and behavior, guarding the inner world of thought as well as the outer world of conduct.

Sefer HaChinuch teaches that this command trains the soul in discipline, ensuring that human desires serve the Torah rather than oppose it (Mitzvah 387). The Talmud links this mitzvah to tzitzis, which are meant to prevent a person from straying after his eyes and heart (Berachos 12b).

Rashi interprets “heart” as heretical thinking and “eyes” as lustful temptation. Ramban adds that the command protects against idolatry, immorality, and arrogance. The Sifrei explains that sin begins when the eye sees, the heart desires, and the body follows, echoing the pattern of Chavah’s temptation in Gan Eden.

This mitzvah therefore guards the most subtle realm of avodas Hashem: the inner world of thought, imagination, and desire.

Rambam

• Hilchos Avodas Kochavim 2:3:
  Following the heart leads to heresy; following the eyes leads to immorality.
• The mitzvah prohibits allowing imagination and desire to wander away from Torah truth.

Sefer HaChinuch

• Mitzvah 387:
  This mitzvah cultivates discipline and purity, ensuring that passions are directed toward holiness.
• A person’s character is shaped by what he allows himself to think about and desire.

Talmud

• Berachos 12b:
  “Heart” refers to heretical thoughts; “eyes” refers to sinful desire.
• The mitzvah is directly tied to the reminder of tzitzis.
• Avodah Zarah 20b:
  The eye sees, the heart desires, and the body commits the sin.

Rashi

• On Bamidbar 15:39:
  “Heart” refers to heresy; “eyes” refers to lustful temptation.

Ramban

• This mitzvah protects against idolatry, immorality, and arrogance.
• It preserves the foundations of Torah belief and moral conduct.

Midrash & Chazal

• Sifrei Shelach 115:
  The eyes and heart act as “spies” for the body, leading it into sin.
• The Midrash compares this to Chavah’s temptation, where sight led to desire and action.

Contrast with Mitzvah 24 — Not to Turn Toward Idolatrous Thought

• Mitzvah 24 forbids directing one’s thoughts toward idolatry.
• Mitzvah 25 forbids straying after personal desires and impulses.
• Rambam explains that one protects against external corruption, the other against internal weakness.

Parallel with Mitzvah 84 — Tzitzis

• Tzitzis serve as a safeguard against straying eyes.
• The Torah explicitly connects tzitzis to this mitzvah: “And you shall see them and remember all My commandments.”
• Ramban explains that mitzvos like tzitzis anchor the heart and eyes in holiness.