The Rishi knew that Indra had not scruples in seeking the companionship of other people's wives. It was therefore, that he used to protect his wife, putting forth all his power.
पुरन्दरं च जानीते परस्त्रीकामचारिणम्॥ तस्माद् बलेन भार्याया रक्षणं स चकार ह।