דברים, פרק י״ג, פסוק א׳

The divine legal system stands as a complete, stable, and perfect structure that requires no human adjustment. True worship demands absolute loyalty to the paths set by God, wholly rejecting any attempt to invent new forms of devotion or integrate foreign customs. Any deviation transforms a religious act into a mere human invention, stripping it of its core essence as the fulfillment of God's will [רש"ר הירש, ביאור יש"ר, שטיינזלץ]. Observance must be comprehensive, treating minor and severe commandments with equal reverence [רש"י, מלבי"ם, משכיל לדוד]. This comprehensive approach inherently relies upon the oral tradition, without which the written law cannot be properly understood or executed [העמק דבר]. The strict language commanding this observance carries the weight of a warning, effectively applying the severity of a negative prohibition even to positive actions, and demanding that every duty be performed precisely as God instructed [רש"י, מלבי"ם, רלב"ג].

When addressing the restriction against adding to the law, commentators draw a distinction between different Biblical instructions. While an earlier directive forbids inventing entirely new commandments to append to the general body of law, this specific warning prohibits adding new details to the structure of an existing commandment [הכתב והקבלה, אדרת אליהו]. Classic examples include inserting a fifth parchment section into phylacteries or taking a fifth species alongside the traditional four species of the palm branch [רש"י, הכתב והקבלה, שפתי חכמים, אדרת אליהו]. Because the terminology of the command is rooted in the concept of speech, this restriction naturally extends to verbal commandments. Consequently, priests are forbidden from appending a personal blessing to the three designated Priestly Blessings [מלבי"ם, אדרת אליהו, מזרחי, גור אריה]. This holds true even if the addition is not physically bound to the original act [גור אריה], or if a person intends to add their blessing only after completely finishing the original requirement [משכיל לדוד, מזרחי].

The desire to add to God's law often stems from a misguided assumption that a person can guess what might find favor in His eyes. However, divine thoughts are entirely unlike human reasoning. Such additions risk spiraling into practices that God actually detests, such as substituting human sacrifice for animal offerings [ספורנו, שד"ל, חזקוני]. Furthermore, when a person introduces a personal modification, they risk performing the act merely to satisfy their own creative addition rather than out of pure submission to God's command, thereby diminishing the purity of the act itself [קונטרס חיבה יתירה, בכור שור]. Conversely, the warning against subtracting demands absolute adherence even when an individual believes they grasp the spiritual rationale behind a law and incorrectly assumes it no longer applies to their specific situation, an error famously made by King Solomon [ספורנו]. This restriction is equally directed at the judicial court, warning them never to declare an existing commandment obsolete [צפנת פענח]. Ultimately, the entire Torah is likened to the natural world; humanity cannot add to or subtract from the fabric of creation, but can only strive to deepen its understanding of it from generation to generation [אם למקרא].

The transition in the text from addressing the community in the plural to addressing the individual in the singular carries a profound message. It emphasizes that the responsibility for the precise preservation of the Torah does not rest solely on the public as a collective. Rather, it is a deeply personal obligation placed upon every single individual, ensuring that the law remains firmly planted in their heart without any deviation [נתינה לגר, אלשיך].