The following great piece on spiritual formation was written by Steve Troxel of God's Daily Word Ministries. It includes some great scriptual references.

Our life in these mortal bodies will always fall short of God's
standard. From the moment sin entered the world, we've been unable to
satisfy God's requirement of perfection. But, knowing our weakness, God
gave His Son as a sacrifice to make perfect those who believe; "By one
sacrifice He has made perfect forever those who are being made holy"
(Hebrews 10:14). Faith in the sacrifice of Jesus makes us perfect forever
- this is the gracious gift of Salvation; "it is by grace you have been
saved, through faith" (Ephesians 2:8).

The grace of God makes us perfect the moment we are saved; but, for the
rest of our days on this earth, we are in the process of "being made
holy." This is why Paul, who freely writes about the gift of grace, can
also exhort us to a life free of sin; "Do not let sin reign in your mortal
body so that you obey its evil desires" (Romans 6:12). Paul understood
that, though we have become "perfect forever," we have also been called to
a high standard of holiness. He therefore refers to his life after
Salvation as a race to be won; "Forgetting what is behind and straining
toward what is ahead, I press on toward the goal to win the prize for which
God has called me" (Philippians 3:12-14).

The picture of a well-conditioned athlete straining toward the finish line
can be a wonderful motivator. However, when we press and strain toward the
wrong goal - or with our own strength - we will soon become fatigued and
discouraged. We are in a race, but we must allow Jesus to establish the
goal as well as the route to be run. The goal of a Christian life must
always be to produce fruit that glorifies God; "This is to My Father's
glory, that you bear much fruit" (John 15:8). And the route of fruit
production must ALWAYS be through the vine of Christ.

John 15:4-5
"No branch can bear fruit by itself; it must remain in the vine. Neither
can you bear fruit unless you remain in Me. I am the vine; you are the
branches. If a man remains in Me and I in him, he will bear much fruit;
apart from Me you can do nothing."

We are called to produce fruit by living a life of holiness and bringing
glory and honor to God in all we do. However, fruit can only grow if we
remain intimately attached to the vine - a branch cannot produce anything
by itself! In our own strength we cannot produce holiness or ANYTHING
esteemed by God. But when we allow the life of the vine to flow through
our veins, we WILL produce a bounty of fruit.

Let's attach firmly to the vine of Jesus Christ and allow Him to flow
though every area of our life. Let's live each day in the holy presence of
God and produce baskets of fruit for His glory and honor. Let's run to win
the race as we press and strain toward the vine.