Tafsir of Al-Furqan 25:51

"And if We had willed, We could have sent..."

He says to His Messenger (ﷺ): "And if We had willed," We would have lightened for you the burdens of warning all the towns. "And We could have sent into every town a warner."

We have restricted the matter to you, magnified you through it, exalted you, and favored you over all other messengers. Therefore, meet this with steadfastness and patience: "So do not obey the disbelievers" in what they want you to do.

By this, He intends to stir him and stir the believers, and to motivate them. The pronoun [in "by it"] refers to the Qur’an, or to the act of not obeying, which is indicated by "So do not obey."

The meaning is: The disbelievers strive and exert themselves to weaken your cause, so meet them with your own striving and exertion, and by biting down on your molars [i.e., persevering], such that you overcome them and rise above them. He called it a "great jihad" because of the immense hardships it entails.

It is also possible that the pronoun in "by it a great jihad" refers to what is indicated by "And if We had willed, We could have sent into every town a warner"—namely, the fact that he is the warner for all towns. For if a warner had been sent to every town, each warner would have been obligated to struggle against his own town. Thus, all those struggles were gathered upon the Messenger of Allah (ﷺ), making his jihad great and magnificent. So He said to him: "And strive against them" —because you are the warner for all towns— "with a great jihad," one that encompasses every form of struggle.

"And it is He who has released [simultaneously] the two seas, one fresh and sweet and one salty and bitter, and He placed between them a barrier and prohibiting partition."