# For the yoke of his burden ... you have broken to pieces as on the day of Midian

"For as on the day when you defeated the Midianites you will set the people of Israel free from being slaves to their oppressors like a person removes a yoke from the shoulders of an animal"

# For the yoke of his burden ... his shoulder ... his oppressor

Isaiah speaks of the people of Israel as if they were one man. Alternate translation: "For the yoke of their burden ... their shoulders ... their oppressor" 

# the beam across his shoulder

The beam is the part of the yoke that goes over the shoulders of the ox.

# beam

Another possible meaning is "staff," a long piece of wood that a person uses to beat the oxen so they will work and a symbol of one person's power to rule other people.

# the rod of his oppressor

Isaiah speaks of the power the oppressor has over the people of Judah as if it were the piece of wood used by a person to beat oxen so they will work.