What is the purpose of the prophets' and messengers' missions?

The wisdom behind sending messengers and prophets is to establish proof against people, so that they will have no excuse on the Day of Judgment by claiming that God's call did not reach them. The evidence for this is His, the Almighty's, saying: "O People of the Scripture, there has come to you Our Messenger making clear to you on [an interval] after [the absence of] messengers, lest you say, 'There came not to us any bringer of good tidings or Warner.' But there has come to you a bringer of good tidings and a Warner." [Al-Ma'idah: 19], and His, the Almighty's, saying: "Messengers who gave good news and warning, so that mankind should not have any argument against Allah after the messengers." [An-Nisa: 165]. This is because Allah sent down His Books and His messengers to clarify the truth, leaving no excuse for anyone who would offer one. As Ibn Mas'ud narrated from the Messenger of Allah, may Allah's peace and blessings be upon him: "And no one loves excuses more than Allah, and for that He sent the prophets as bearers of good tidings and as warners."