In "God's Word for Today" Gordon Snider writes:

“The check is in the mail.” There is likely no other promise received with so much skepticism as this one. We have heard the promise before, and it didn't prove true. We will believe it when we see the check. Many people hear the promises in the Bible with the same skepticism. The promises seem too good to be true. In fact, Isaiah was facing the same response to his ministry. God was making great promises to His people through the prophet, but the future seemed to contradict the assurances of good. So in 61:11 Isaiah raised the problem dealt with in our lesson today: “How can I be sure that the good God has promised will really happen?” In our lesson today, God's Old Testament people were facing captivity and the destruction of Jerusalem – the holy city. The modern church is facing renewed persecution from without and increased apathy from within, either of which potentially could destroy our “holy city.” Still, some people say that “the future is as bright as the promises of God.” How can they be so sure? The answers Isaiah gave to the Old Testament church are relevant to the New Testament church as well.

Source: Building Christian Relationships: Adult Teacher's Insights, page 10.