The Gospel and Lifestyle - how one vindicates the other

When I start blogging, it's because I'm preparing a sermon, and bits of prep sort of fall of my desk and into my blog.
Evangelicals love to find ways of compelling a godly life out of themselves, and one is that a godly life vindicates the gospel. We speak the gospel and then show that it is true by the transformed life that we lead.
I've just come to the conclusion that such an argument is backwards (I'm an amateur, I'm slow!) Rather, the process works the other way round. I hope in the gospel, which has lifestyle implications. This hope that is in me arouses questions (1 Peter 3:15) and so I explain how my hope is vindicated by the gospel. The psalmist in Psalm 102:12-15 looks forward to his and others hope (v14) in the eternal God (v12) being vindicated by His restoring Zion (v13), a vindication of hope that will lead to the nations turning to God. The vindication of their hope was future: but to us that same event is past - it is the incarnation, atonement, resurrection and ascension of Jesus Christ.
That has wonderful implications. Firstly, it means I can sin. No, not in the sense that I'll be lazy about holiness. But when I do sin, I won't think that my evangelism is dead. Rather, the fact that my hope is not destroyed by my sin will raise the question, "what can vindicate such a hope?" Answer: Christ. Secondly, it means I can pursue holiness in freedom. My heavenly citizenship is secure, because of Christ, a hope vindicated by the events of His ministry. So in that assurance I live my new citizenship. What vindicates living differently to others? Answer: Christ. Suddenly the gospel is about Jesus again.

Why does Hebrews 1 quote Psalm 102?

Here's a thought I had: comments?

In Psalm 102:25-27, the exile is speaking in faith of his God, that his God is the everlasting, unchanging Creator God; in Hebrews 1:8-12, in which this verse is applied to the Son, the Father is speaking. So what is the writer to the Hebrews doing?
In order to believe in his situation that Zion really can be restored, the exile needs to believe that his God is the unchanging, faithful, everlasting Creator God, fully able and fully faithful. In order to believe that His Messiah can really achieve the mission for which He has appointed Him, that of second Adam and therefore restorer of Eden itself, of Zion, the City of God with men, then God Himself must be able to express similar faith in the Messiah! What the writer to the Hebrews therefore implies is that his readers may have full faith in the Lord Jesus because He is the one of whom God the Father may speak precisely those words of faith that they have been speaking of God since the exile.