It is not defined what kind of sin may be punished so severely and why exactly the clergyman are granted so much power over their wives. The council deals mainly with the Priscillianist heresy, so probably Canon 7 should be read as an official reaction to the egalitarian ascetic movement which especially attracted women (Hillner 2015: 160). The involvement of some of the clerical wives into the new forms of asceticism might have been interpreted as scandalous and disgracing the honour of the clerical office (Burrus 1995: 112-113).
The phrase praeter necem is difficult to interpret. It can mean that the clerical prerogatives to punish their wives are not applicable if they committed murder. On the other hand, praeter necem may be understood as referring to the remark about "salutary and not fatal fasting". In other words, it would forbid clerics to kill their sinful wives.