Timothy, my son, I am giving you this command in keeping with the prophecies once made about you, so that by recalling them you may fight the battle well, holding on to faith and a good conscience, which some have rejected and so have suffered shipwreck with regard to the faith. 1 Timothy 1:18-19
Why is it that Christians, especially those in leadership positions, sometimes mess up in big ways? Why do some fall so far that they even lose their faith?
Of course, for each individual the story will be different. But I suspect that in the majority of cases the root cause was a failure to maintain the important priorities. As Stephen Covey once put it:
The main thing is to keep the main thing the main thing.
I have seen Christians become totally immersed in interests outside the Christian community. They begin to get involved in some secular activity in order to meet people with whom they can share their faith. But they forget to guard their hearts and gradually become corrupted by the world they set out to reach.
Others have a personal passion which becomes more important than the Lord Jesus. When there's a choice between Sunday worship or their hobby, the hobby wins out every time. Little by little they lose the desire to meet with God's people for worship.
In some cases it is more subtle - an obsession with a particular ministry or doctrine. Time which should be spent in the treasure chamber of the prayer closet is spent "working for the Lord," or "studying the Bible." In reality the ministry or the study, which was founded on godly direction has become an idol. Love for the work or the study has replaced love for Jesus. The personal relationship begins to slip but everything on the surface seems fine. Nobody notices until, apparently suddenly, another saint walks away from the faith.
In all these circumstances the main thing has ceased to be the main thing.
So what is the main thing for the Christian?
It is expressed very clearly in Micah:
He has shown you, O man, what is good.
And what does the Lord require of you?
To act justly and to love mercy
and to walk humbly with your God. Micah 6:8