Besides, God has already addressed this topic in the Quran.
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Surah 6:158
Do they then wait for anything other than that the angels should come to them, or that your Lord (Allah) should come, or that some of the Signs of your Lord should come [/FONT] [FONT=Georgia, Times New Roman, Times, serif](i.e. portents of the Hour e.g., rising of the sun from the west)! The day that some of the Signs of your Lord do come, no good will it do to a person to believe then, if he believed not before, nor earned good (by performing deeds of righteousness) through his Faith. Say: "Wait you! we [/FONT][FONT=Georgia, Times New Roman, Times, serif](too) are waiting." Verily, those who divide their religion and break up into sects (all kinds of religious sects), you (O Muhammad SAW) have no concern in them in the least. Their affair is only with Allah, Who then will tell them what they used to do.
[/FONT]Basically, when he does come, it'll be for judgement and way too late. The whole point was to believe in in God from the unseen. Otherwise faith would be much of a test, just a Holy Rule on earth, defeating the concept of free will, good and evil.