The Seventh Day Advent Hoppists were a Christian sect to which Arnold Rimmer's parents belonged.
Mr and Mrs Rimmer were very religious, taking the Bible scriptures at face value. The Hoppists were primarily concerned with a particular verse from the New Testament. St. Paul's first epistle to the Corinthians, chapter 13, verse 13 had been misprinted in a certain edition of the Bible. In their version, the verse read "And now these three remain: Faith, Hop and Charity. But the greatest of these is Hop".
The Hoppists took this literally and insisted that their followers spent every seventh day hopping. They would hop to church, hop through the service and then hop home again. The Rimmers even served their Sunday lunch whilst hopping, causing them to wear protective clothing to avoid burning themselves.
Arnold Rimmer did not share his parent's beliefs, but refused to deny their rights to hold those beliefs. (RD: The Last Day)