Who should partake at the Memorial — and what is the new covenant?

Luke 22:28-30 shows Jesus making a covenant with a specific group — those who stayed with him in his trials — promising them thrones. 1 Corinthians 11:25: the cup "represents the new covenant." The new covenant, like the Mosaic covenant, is with a specific group — not all believers automatically. Questions: Was John 6:53-54 about a ceremony, or about faith (see John 6:40)? What does the Day of Atonement parallel tell us (only the high priest entered the Most Holy)? What does the spirit witness of Romans 8:15-16 confirm? nwtprogress.com