Certainty

And I am sure of this, that he who began a good work in you will bring it to completion at the day of Jesus Christ.
Philippians 1:6

This is a verse which broadcasts Paul's understanding of Christian dependence and which also highlights the incredible hope he had for the Philippian believers. Paul knew something that many of us miss - that our faith journey and our progress in becoming more like Christ (sanctification) are works of God. While we certainly have the responsibility to believe and to strive for holiness, unless God is at work, any attempt on our part will be futile. Therefore, when we are struggling with our beliefs or when we are feeling crushed by our addiction to a particular sin, perhaps the best place to begin is on our knees in front of the God who works in us.
Furthermore, Paul was also filled with hope - not merely "wishful thinking" hope but certain or confident hope. He knew and trusted that the God who had started working in them was going to finish His task. Their salvation would be realized.
May we learn to lean on God for our progress in the Christian faith, and may the Spirit fill us with confidence that we are in good hands - hands that will complete the task He has begun.