“Not that I have already obtained it or have already become perfect, but I press on so that I may lay hold of that for which also I was laid hold of by Christ Jesus. Brethren, I do not regard myself as having laid hold of it yet; but one thing I do: forgetting what lies behind and reaching forward to what lies ahead, I press on toward the goal for the prize of the upward call of God in Christ Jesus. Let us therefore, as many as are perfect, have this attitude; and if in anything you have a different attitude, God will reveal that also to you; however, let us keep living by that same standard to which we have attained.” Philippians 3:12-16
You can take almost any scenario in life - cleaning house, building a house, raising kids, working at a job - and understand that each area needs maintenance. It is not enough just to do something once and expect that it will forever keep working, stay fixed, stay clean, or take care of itself. Everything and everyone needs to be nurtured to keep on track. The same is true of our Christian faith.
It is a terrible misconception to believe that personal growth for a Christian believer is natural and easy. Pressing on in our faith requires hard work and effort.