# He was oppressed

"They treated him harshly" 

# he did not open his mouth

"he did not protest"

# as a lamb that is led to the slaughter, and as a sheep that before its shearers is silent

Isaiah compares the servant to a lamb and a sheep to emphasize that he will remain silent as people harm and humiliate him.

# as a lamb that is led to the slaughter

"just as a lamb is silent as a person slaughters it"