Some of the people who saw Jesus resurrect Lazarus reported to the Pharisees. The Pharisees worried that people believing in Jesus would result in them losing their standing.
Eventually, Caiaphas (the high priest) talked about how it is "expedient for [them] that one man should die for the people" rather than the nation (11:50). Based on the following verses, Caiaphas's statement was mainly a prophecy on how Jesus would later die for nation (and to gather the scattered people of God). Later on, we'll see that Jesus died for the Judeans on the cross (thereby taking on their punishment on their behalf) and also the entire world, and we'll also see how Jesus fostered a community of worldwide believers who shared Jesus through words and actions.
However, some people took Caiaphas's words to mean that killing Jesus would save the kingdom. As a result, those people plotted to capture Jesus to put in to death. The Pharisees also told people to report if they see Jesus, much like someone on a wanted sign. Eventually, Jesus did not walk openly with the Judeans for a while (though he would later return, resulting in his capture that lead to the redeeming sacrifice as prophesized by Caiaphas).