If for some faith is enough, then why did Jesus spend his time on earth preaching.Did the preachings have....?

...no meaning or were unessential. If Jesus's 12 apostles had some flaws in them as some say, why did he entrust such a big responsibilty of spreading the gospel on them. Would not the all knowing Jesus the Son of God himself find the right people? Why did he as they say reappear to Paul but let his 12 apostles get executed? If the 12 apostles were at the Last supper and Paul wasn't then why not even one of the 12 talk about it or introduce that liturgy of bread and wine but Paul did although Peter was the rock? Why did the Bible the inerrant word of god raise so many contradictory questions?