The history of all peoples, individuals and nations, in our own time also and in our own lives has a certain pattern. The words of God’s spokesman are about this but with the twist that God can always be relied upon to bring bightness and joy after it all.
Even in the early church there were divisions among Christians with different takes on what it meant to be a Christian. Paul writes to such Christians in Corinth. He says all should remember that it is Christ who died for them and whom they should together follow!
The gospel picks up on the ideas of the first reading – seeing Jesus as the light for all. But it also tells us of discipleship – those called may be quite different from each other but are called equally to follow Jesus in their new life.
Further background can be found here.