Through verse 1 and 2, Isaiah is talking about God clearing a field of stones and planted a vineyard to yield good grapes, built a tower to defend the vineyard and a winepress to turn the grapes into wine. When it was the time of harvest, he looked for crops of good grapes; but he learned that it only yielded bad grapes.
The field is the Promise Land, the stones are the Canaanites, whom the Lord wiped out, the vineyard is Israel, the tower is God's protection on Israel, the good grapes are people who want to obey God, and the bad grapes are people who ignored and disobeyed God.
Through verses 3 and 4, God said, "Now you dwellers in Jerusalem and men of Judah, judge between me and my vineyard. What more could have been done for my vineyard than I have done for it? When I look for good grapes, why did it yield only bad?"
At that time, Israel was becoming a very evil nation like it's neighboring nations. And God wasn't happy with them at all. So God sent Isaiah to warn them of what was to come if they continued their wickedness. Thankfully, because of the faith of King Hezekiah, they listened to the warnings. And because of their obedience, God didn't bring destruction to them during King Hezekiah's reign.
In my next post, I will finish talking about verses 5-7. To understand more about it, read Isaiah 5:1-7.