Why did Jesus die?
To give His life a ransom for many
Matthew 20:28 (ESV)
“even as the Son of Man came not to be served but to serve, and to give his life as a ransom for many.”
To remit the sins of many
Matthew 26:28 (ESV)
for this is my blood of the covenant, which is poured out for many for the forgiveness of sins.
To take away the sin of the world
John 1:29 (ESV)
The next day he saw Jesus coming toward him, and said, “Behold, the Lamb of God, who takes away the sin of the world!
To save the world
John 3:17 (ESV)
For God did not send his Son into the world to condemn the world, but in order that the world might be saved through him.
To give His life for the sheep
John 10:11 (ESV)
I am the good shepherd. The good shepherd lays down his life for the sheep.
To gather together into one, the scattered children of God
John 11:49-52 (ESV)
But one of them, Caiaphas, who was high priest that year, said to them, “You know nothing at all.  Nor do you understand that it is better for you that one man should die for the people, not that the whole nation should perish.”  He did not say this of his own accord, but being high priest that year he prophesied that Jesus would die for the nation,  and not for the nation only, but also to gather into one the children of God who are scattered abroad.
To cast out the Prince of the world
John 12:31 (ESV)
Now is the judgment of this world; now will the ruler of this world be cast out.
To lay down His life for His friends
John 15:13 (ESV)
Greater love has no one than this, that someone lays down his life for his friends.