(Greek θέλημα) Willpower.
“Father, if thou be willing, remove this cup from me: nevertheless not my will (Thelema), but thine, be done.” —Luke 22: 42
So (Father), "do what thou wilt (Thelema), shall be the whole of the Law." And what is the whole of the law?
”Jesus said unto him, Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind. This is the first and great commandment. And the second is like unto it, Thou shalt love thy neighbour as thyself (who is thy Father, thy true Self).” —Matthew 22: 37-39
On these two commandments hang the whole of the law and the prophets.
"[The rune] Dorn, Thorn, signifies willpower. Remember Gnostic brothers and sisters, that our motto is Thelema. The divine Rostrum crowned with thorns signifies Thelema, that is to say, conscious will." —Samael Aun Weor, Magic of the Runes