# But it is to the extent of your hardness and unrepentant heart

 "But because you are stubborn and refuse to repent"

# you are storing up for yourself wrath

"you are making your punishment worse". The longer they go without repenting, the more severely God will punish them. 

# on the day of wrath ... the day of the revelation of God's righteous judgment

"when God will show everyone that he is angry and that he judges all people fairly"