This week's Torah portion tells the story of Pinchas who showed loyalty and bravery for God. At the advice of the evil prophet Balaam, the daughters of Moab and Midian tempted the Jews to sin with them, then led them to worship their idols. Pinchas did not act within the bounds of Jewish law when he killed Zimri as there was no Jewish court involved in investigating the case.
He was criticized for killing Zimri without asking Moshe and the other sages. However, God rewarded Phinehas for his bravery by giving him eternal priesthood.
The Third Noahide Commandment is about Forbidden Relations. Both prostitution and any kind of pre-marital relations could be destructive to the human being. This refers to Jews and non-Jews as well. A Noahide couple should seek a long-term relationship within a legal marriage.
Actual worship of idols is banned for Noahides too as they have to be aware of the oneness and unity of God. Pinchas is actually linked to Elijah the prophet and played a key role in a number of later events in Jewish history. He will be the one to announce to the entire world that the time of redemption has arrived.
With thanks to the writer: Rabbi M. Bernstein