Proverbs 17:17 - Matthew Poole's English Annotations on the Holy Bible

A friend, a sincere and hearty friend, loveth at all times, not only in prosperity, but also in adversity, when false friends forsake us. A brother, who is so not only by name and blood, but by brotherly affection, is born for adversity; was sent into the world for this among other ends, that he might comfort and relieve his brother in his adversity. So this proverb compareth a friend with a brother, and showeth that a friend doth that freely, and by choice, which a brother doth by the force and obligations of nature. But this last clause may be, and is by divers, otherwise rendered, and he (to wit, the friend) is born a brother (or, becomes or is made a brother, i.e. puts on brotherly affection, as if he had received a second birth, and was born his brother; such expressions being not unusual, both in Scripture and in other authors) in or against the time of adversity. So the sense is, He is a friend at all times, but in adversity he is more than all ordinary friend, even a brother.