Torah Mitzvah A King May Not Marry Too Many Wives

Sanhedrin 21a:

(Mishnah): "V'Lo Yarbeh Lo Nashim" (Devarim 17,17) - a King may not marry more than 18 wives

(Gemara): Question: What is the source that only up to 18 wives are allowed? Answer: (Shmuel II: 3,2-5) David had (children from) six wives "Amnon la'Achino'am...veha'Shishi Yisre'am l'Eglah." Later the prophet Nasan told Dovid (12,8) "V'Osifah Lecha ka'Henah vecha'Henah (and add to you like them and like them)." Telling Dovid a limit on the number of wives – can add another six (just like the first six wives already taken) and even another six, a total of 18.

Thus, this mitzvah contains the concept of three groups of six.

Another set of three groups of six:

SHMONEH ESREH (18 BLESSINGS DURING AMIDAH)
ESTABLISHED BY THE LEADERS OF THE GREAT ASSEMBLY
(19TH BLESSING ADDED SEVERAL CENTURIES LATER)

PRAISE שבחMIDDLE TWELVETHANKS הודאה1. HISTORICAL4. KNOWLEGE16. ZION2. MANIFESTATIONS5. RETURN17. GRADITUDE3. HOLINESS6. FORGIVENESS18. PEACE7. REDEEM8. HEALING9. MATERAIL SUCCESS10. INGATHERING11. JUDGEMENT12. FAITH IN THE RIGHTEOUS13. YERUSHALIM14. MOSHIAH15. HEARS PRAYERS

INDIVIDUAL REQUESTS COMMUNAL REQUESTS