Why did the Prophet, peace and blessings be upon him, not participate in the fighting with the Companions despite his strength? And was his saying, "Who will repel them from us?" for encouragement, tactical withdrawal, or self-preservation?

It is permissible for a Muslim to ask questions to remove doubts, while revering the Prophet (peace be upon him). Courage is not measured by the number of killings, but by the steadfastness and strength of the heart. The Prophet (peace be upon him) was the bravest of people, as testified by Ali ibn Abi Talib. The Prophet (peace be upon him) did not kill anyone with his own hand except Ubayy ibn Khalaf on the day of Uhud. Thus, his courage lay in the steadfastness and strength of his heart, not in frequent killing. The Prophet's (peace be upon him) command to his companions to fight was not out of fear for himself, but to establish the right of support, reverence, and honor, and to convey the message he was entrusted with. He also was keen not to kill disbelievers except out of utmost necessity, because whoever is killed by a prophet will be among those who suffer the severest torment on the Day of Judgment.