An-Naḥl: 94
"And do not take your oaths..."
Then, He repeated the prohibition against using oaths as a means of deception (dakhal) among them, to emphasize the command and to demonstrate the gravity of what results from it:
"Lest a foot should slip after it was firmly planted"
Meaning: Your feet will slip away from the path of Islam after having been firmly established upon it.
"And you taste evil"
In this world, by turning others away from the path of Allah and exiting the religion yourselves. Or, it may mean your turning others away; for if they were to break the oaths of allegiance and apostatize, they would establish the breaking of oaths as a precedent for others to follow.
"And for you is a great punishment"
In the Hereafter.
"And do not exchange the covenant of Allah for a small price. Indeed, what is with Allah is best for you, if you only knew."