I have seen the foolish taking root. The "I" is emphatic. "I myself have seen," etc. What Eliphaz had seen was that folly, i.e. sinful infatuation, was always punished. It might seem to prosper: the foolish man might seem to be taking root; but Eliphaz was not deceived by appearances—he saw through them, he knew that there was a curse upon the man's house, and so pronounced it accursed.
And the ruin which he had foreseen, it is implied, followed. But suddenly; rather, immediately, without hesitation. I cursed his habitation; i.e. "pronounced it accursed, declared that the curse of God rested upon it?"