It contrasts "foe and friend," just as the sonnet contrasts "love and hate."
We are natural enemies; and when your foe is disabled, then is the time to strike.
By this time, the first of August, we knew more about the foe we were to meet.
They lie at the mercy of every foe, of every passion, of every change.
You were friendless, and the man who has all earth for a foe befriends ...