This is the first post in a series on Faith and Doubt.
Christianity is not a religion.  It’s Good News.  Everything I will say about faith, doubt and salvation in this series will hinge on this distinction.  I borrow it from Timothy Keller (with minor revision).
So let’s outline the distinction between religion and Good News.
Religion tells us what to do to win God’s approval or to draw closer to God or to accomplish God’s purposes on earth.  Codes of moral conduct, instructions for worship and programs for social action tell us what we have to do in order to get right with God.
Good news is, well, news.  It reports to us what God has done for us already.  On the Cross God extends unwarranted mercy.  The news is that we don’t have to do a thing to justify our existence.  God has already done that.
Religion sets us on the path of moral and spiritual achievement.
Good News frees us from the burden of measuring up through our achievements.  Jesus accepts us as his followers when we recognize that we need him and we rely on him to come through for us.

To put this a slightly different way, being a Christian means asking Jesus Christ for mercy.  
We’re not asserting our rights or demanding our just deserts.  We are plainly and honestly stating our need, admitting our inability to meet this deepest need, and with paradoxically calm confidence trusting Christ himself to give us what we need.
In other words, salvation is a gift of God’s mercy.  There is nothing we can do to achieve it, to earn it.  
We just need to believe.
And here of course is the rub.  Plenty of us believe.  We just need help with our unbelief.  Doubts creep into our heart and minds.  
In fact, some of our doubts don’t creep in at all.  Some of us have dearly held opinions about nature or human existence or culture or moral law that seem to contradict what Christians believe.  
Others read the Bible and find primitive attitudes or implausible stories or pre-modern conceptions about the world.  Some just can’t see how a book like this could be authoritative for anyone with even the slightest bit of 21st century sophistication.
Do thoughts like this condemn us? Must faith exclude doubt in order to count for our salvation?
We’re on the verge of making a common error when thinking about faith.  We’re about to turn it into an achievement.  We’re leaving one last sector for ourselves to win over God with our achievements: our intellectual life.
In the next posts, we will get our heads around what faith is and what it is not.  Then we’ll look at varieties of doubt.  
As we will see, some forms of doubt are a healthy part of our intellectual life and have no negative impact on our relationship with Christ.  By contrast, there is at least one species of doubt that drives a wedge between God and us.