81. The verse may also mean that the obedience expected of the believers is of recognized and well known type, which is above every kind of suspicion, and not such as may need swearing of oaths to convince others of its sincerity. Their conduct is manifest and everybody who comes into contact with them feels that they are truly obedient to Allah and His Prophet.
82. That is, you might succeed in deceiving the people, but you cannot deceive Allah, Who is aware of everything, open or hidden, even of your innermost motives and intentions.