In "The Crucible", Reverend Parris is worried that Abigail's actions have jeopardized something important. What is jeopardized?

There are actually three instances in the play that your question can be referring to.

The first one occurs in the beginning of Act One when Rev. Parris realizes what the girls were doing in the forest the night before and notices that many people are going to blame their actions (and the results of those actions) on witchcraft. If this is to happen (and it does happen) then Abigail's actions have jeopardized his position and power as Salem's reverend.

The second instance occurs in the same act when Parris questions Abigail about her involvement with John Proctor. It is revealed in this act that Abigail and Proctor have had an affair, and this has seriously jeopardized Abigail's good name in the village. Goody Proctor will not go anywhere near Abigail and has obviously told the other women of the village that they should not hire Abigail as their house servant.

The final instance occurs between Acts Three and Four when the reader finds out that Abigail and Mercy Lewis have stolen money from Parris and have fled Salem. At this point Rev. Parris thinks that his life has been jeopardized, especially since someone has stabbed a dagger into his door. He feels that once everyone finds out about Abigail's actions they will blame the entire situation on him because it was his house where the witchcraft was originally discovered.