What is the standard by which Allah chooses prophets and messengers, and does man have a role and choice in that, or is it a favor and a blessing?

Allah, the All-Wise, the All-Knowing, chooses for prophethood the most righteous and fitting individuals. Messengers are the elite of creation, and their selection is based on Allah's knowledge that they are worthy of it, and that divine revelation will be fitting for them. Prophethood is a divine grace and a heavenly gift; it is not acquired through effort or attainment. Allah knows best the ground suitable for planting the tree of grace. Thus, the Prophets did not attain this rank through their own diligence, but rather through Allah's favor upon them and His choosing them. They are the best of all humanity, and Allah has gathered for them every virtue from all its aspects.