# fall away

"leave me"

# for it is written

"for the prophet Zechariah wrote long ago in the scriptures" 

# I will strike

Here "I" refers to God. It is implied that God will cause or allow people to harm and kill Jesus.

# the shepherd ... sheep of the flock

This refers to Jesus and the disciples. 

# the sheep of the flock will be scattered

"they will scatter all the sheep of the flock" or "the sheep of the flock will run off in all directions"