question #1 Sahih al-Bukhari 3078, 3079, Book 56, Hadith 283 : What is the significance of the pledge of allegiance in Islam?

Mujashi (bin Mas`ud) took his brother Mujalid bin Musud to the Prophet (ﷺ) and said, “This is Mujalid
and he will give a pledge of allegiance to you for migration.” The Prophet (ﷺ) said, “There is no migration
after the Conquest of Mecca, but I will take his pledge of allegiance for Islam.”