[Explanation]
The author—may Allah have mercy on him—said: “Chapter: The virtue of loving for Allah’s sake and hating for His sake, informing someone that you love him, and what you say to him when you tell him.” These are four topics, and the author, may Allah have mercy on him, cited the proofs that establish them.
He, may Allah have mercy on him, began with the words of Allah the Exalted: “Muhammad is the Messenger of Allah, and those who are with him are stern against the disbelievers, merciful among themselves” (al-Fath 48:29).
“Muhammad is the Messenger of Allah,” and those who are with him are his Companions. “Stern against the disbelievers” means they are strong and firm toward the disbelievers; “merciful among themselves” means each of them shows mercy to the others.
“You see them bowing and prostrating, seeking bounty from Allah and His pleasure.” In other words, when you observe them in prayer you find them in bowing and prostration, humbled before Allah and drawing near to Him. They desire nothing of worldly gain; rather, they seek bounty from Allah—that is, reward—and His pleasure, meaning His good pleasure.
“Their mark is on their faces from the trace of prostration”—their distinguishing sign appears on their faces as an effect of prostration. This sīmā is the light of the face, the radiance produced by their prostration to Allah. It is not the physical callus that may form on the forehead; that callus might indicate frequent prostration, yet the real sign is the brightness of the face.
“Their mark is on their faces from the trace of prostration; that is their description in the Torah”—that is, this is how they are described in the Torah. Allah, exalted is He, praised this community and its Messenger ﷺ and mentioned their qualities in both the Torah and the Gospel, as He says: “Those who follow the Messenger, the unlettered Prophet, whom they find written with them in the Torah and the Gospel, who enjoins upon them what is right and forbids them from what is wrong…”