The answer is: Thou shalt not commit adultery

Exo 20:14

The seventh commandment, "Thou shalt not commit adultery," stands out in the Exodus narrative as a crucial moral guideline that promotes fidelity and trust in human relationships. While it addresses the serious issue of marital commitment, it also serves as a broader reminder of the value of loyalty and integrity in all kinds of relationships.

Interestingly, the context of this commandment highlights the importance of family in the ancient Israelite culture—a family unit foundational to their society. Adultery could unravel the social fabric, impacting not just individuals but community cohesion. In a way, this commandment encapsulates a holistic view of social responsibility and personal respect for others.

Echoes of this principle can be found in different cultural texts as well. The ideal of fidelity is echoed in literature, poetry, and diverse societies cross the ages, suggesting that humanity has always recognized the value of commitment in bonds, regardless of temporal changes.

Additionally, the command itself reflects ancient wisdom passed through oral tradition long before it found its written form. Scholars have noted how such ingredients of ethics can rise with distinct expressions within cultures and religions, shaping moral reasoning through generations. The presence of a societal 'sacred moral code,' much like our modern sense of ethical guidelines, reveals humans’ deep yearning for a structured and dignified approach to living harmoniously.

Thus, the seventh commandment stands as a perennial lesson—promoting love, trust, and above all, the harmony essential in fostering strong communities.