What is the meaning of Isaiah 1:17? Defend the oppressed. Take up the cause of the fatherless. Plead the case of the widow. (NIV)


What does those three things mean?
An how do you do such things?

I would surely appreciate an explanation...
Isaiah 1:10-12
 tells us that those words were addressed to the rulers and priests. These people were to judge cases brought before them righteously, in the "courts," as it says in verse 12. But they have not sought justice, punished the oppressors, nor sided to help the widows who have no husbands to defend them and help them. 

Verses 21-26 tells us about their wretched ways, that they cared nothing about justice, but they were "companions of thieves," loving bribes. 

In conclusion, the passage you quote is God telling them to turn back to dealing righteously in the courts, to take up justice again.