Messages are displayed, by default, in reverse chronological order (most recent at the top).  

A new comment on a message causes it to move up in the feed (unlike "likes").

A message can also be moved up manually by clicking on the "Move this message up" arrow icon.

Finally, a message can be pinned by a sphere administrator (or a "publisher"), which allows the message to be displayed at the top of the feed for sphere members.

  

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