This proverb implies that you should work with dedication and loyalty for others, even if it seems like a selfless effort for someone who typically benefits from your efforts. The comparison of working for your father-in-law as if for your son-in-law suggests that sometimes you must carry out tasks without expecting direct recognition, knowing that your work’s fruits will be rewarded in one way or another. In English, an equivalent proverb might be: ‘A job well done is never lost’.