Salvation: what needs to happen?

I've already posted on the reading for Hebrews for today, but the more I read this passage, the more a discussion ensued in my own mind.
I kept reading some online commentaries, and lo and behold, there was a phrase in Hebrews 5:9 that I skipped over without any thought.  "He [Jesus] became the source of eternal salvation for all who obey him".
Clarke's commentary states that "he is the author and cause of eternal salvation only to them who obey him. It is not merely believers, but obedient believers, that shall be finally saved."  This commentary is saying that we are ultimately only saved by being obedient to God and following his commands to go out into the world and preach the good news, grow in faith, and enlarge the kingdom of God here on earth.  Does this mean that we must do more than just believe on the Lord Jesus Christ to be saved?  Does believing in Christ encompass all these good works, or does it necessarily lead to these actions if you do truly believe in Christ?  What does obedience to Christ mean?   I believe this passage is saying that Christ has become the perfect Saviour for us and to receive this salvation, we must obey him.  Obedience means to follow his commands, and he has commanded us to believe in him as Saviour for us to be saved.  He has also commanded us to repent, and confess his name, and preach the good news.
There is a short little compilation of verses on this topic that can be found at this location.  Let me know what you think about salvation and what it entails or requires.  Jesus Christ did say to the thief on the cross that on that day, he would be with him in paradise.  Does that mean the thief believed in Christ and obeyed his commands?