An-Nur: 53
"And they swore by Allah their strongest oaths..."
"Their strongest oaths" (jahd yamīnihim): A metaphor derived from "exerting one's self" (jahd nafsihi), which is when one reaches the utmost limit of their capacity. This applies when one exaggerates in an oath, reaching the peak of its intensity and firmness.
Ibn Abbas (may Allah be pleased with him) said: "Whoever says 'By Allah' has sworn his strongest oath."
The origin of the phrase "He swore the strongest of oaths" (aqsama jahd al-yamīn) is "He swore, exerting the oath with exertion" (aqsama yajhadu al-yamīna jahdan). The verb was omitted, the verbal noun (masdar) was brought forward, and it was placed in the position of being annexed to the object, similar to His saying: "So strike the necks" (fa-darb al-riqāb). The status of this accusative is that of a state (hāl), as if he said: "Exerting their oaths."
"Known obedience" (tāʿah maʿrūfah): This is the predicate of an omitted subject, or a subject whose predicate is omitted. It means: "What is commanded of you and what is requested of you is a known, recognized obedience, in which there is no doubt or suspicion—like the obedience of the sincere believers whose inner state matches their outer appearance—not oaths you swear with your mouths while your hearts are contrary to them."
Alternatively, it means: "Your obedience is a 'known' obedience, in that it is mere speech without action." Or: "Known obedience is more exemplary and better for you than these false oaths."
Al-Yazidi read it as tāʿatan maʿrūfatan (in the accusative case), meaning: "Obey with an obedience."
"Indeed, Allah is Acquainted" (inna Allāha khabīr): He knows what is in your consciences, and nothing of your secrets is hidden from Him. He will inevitably expose you and recompense you for your hypocrisy.
"Say, 'Obey Allah and obey the Messenger; but if you turn away - then upon him is only that [duty] with which he has been charged, and upon you is that with which you have been charged. And if you obey him, you will be [rightly] guided. And there is not upon the Messenger except the clear notification.'"