John 6

Jesus answered and said to them, “This is the work of God, that you believe in Him whom He sent.” v.29

Read chapter 6
This chapter is packed with so much good stuff!  Yet I think this one verse sums up a lot of what this chapter is portraying.  After 5,000 men were fed miraculously, they desired to be fed continuously.  Jesus goes on to tell them that He is the bread from heaven and that through Him one will never hunger again.  The people believe that Jesus is The Prophet that Moses spoke about that would come, the understand the truth right in front of them, but the are uninterested.  They keep asking to be filled by what cannot fully satisfy.  They seek Jesus only because He provided immediate fulfillment of food and Christ challenges them to labor for food that endures to everlasting life.  So they question what works they should do to do God's work for this (they're finally getting it).  And the best answer ever is, "THE work of God, that you believe in Him whom He sent." Bam!  Only one thing they must do for this eternal life: believe.  So many religions and sects of Christianity are works based salvation, but our God only desires ONE work and that of the mind to believe that Jesus was sent by God.  No other work can please God like this one can or be substituted for eternal life.  Have you believed the lie of saved by works?  Why is this so hard for people to think they have to do works to be in God's favor?