# will also drink some of the wine of God's wrath

"will also drink some of the wine that represents God's wrath" 

# that has been poured undiluted

This means that the wine has no water mixed into it. It is strong, and a person who drinks much of it will get very drunk. As a symbol, it means that God will be extremely angry, not just a little angry. 

# cup of his anger

This symbolic cup holds the wine that represents God's anger.