God hears our prayers.  Why does He answer some with "yes" and some with "no"?  We will always be asking this question because God does not think like we think (Isaiah 55:8).  God reveals some things to us and some things He leaves mystery.  Isaiah 65 is about answers.

In the previous chapters of Isaiah, the remnant was allowed to bring their complaints and fears and repentances to God.  Now, in chapter 65, God answers them.  Look at His words:

"I permitted Myself to be sought by those who did not ask for Me." (vs 1)
"I have spread out My hands all day long to a rebellious people." (vs 2)
"I will not keep silent, but I will repay." (vs 6)
"I spoke, but you did not hear." (vs 12)

And here is the picture of cooperative grace:

Verses 18-19 say, "But be glad and rejoice forever in what I create, for behold, I create Jerusalem for rejoicing, and her people for gladness.  I will also rejoice in Jerusalem, and be glad in My people."

Do you see why God created Jerusalem?  "for rejoicing"
Do you see what God will do because of Jerusalem?  "rejoice"

We are created in God's image.  To fully understand that, we do not need to know all the answers to all the mysteries, we simply need to begin fulfilling our purpose.