Ethos is the distinctive essence of a culture, era, or community as shown in its beliefs and ambitions. Some synonyms are character, atmosphere, and mood.
Spiritually: the culture of God’s Kingdom comes from Heaven itself, from the words of the Holy Spirit in the Bible, from the love of God and Jesus. We’re to be very happy in the Lord, and again, be very happy (Philippians 4:4). As Jesus modeled on earth, His kingdom is full of love, good works, and worshiping God, and all eyes are to focus on heavenly things more than earthly things (Col. 3) …ethos.
(Of course, if there are citizens in God’s kingdom who don’t behave in sync with the ethos, they are aliens, criminals, spies, whatever…)