Not that I have already attained, or am already perfected

Philippians 3:12
Not that I have already attained, or am already perfected; but I press on, that I may lay hold of that for which Christ Jesus has also laid hold of me. 

We have heard about the process of sanctification which we are suppose to go through when we belong to Christ and we mature. Sanctification itself is not the end goal, perhaps it can be thought of as a guide as to how we are walking with God - whether we are maturing or drifting. The end goal then, as always has been, is to be back in a relationship with God. It is about truly recognizing God as our Father and being restored to Him.

Let perseverance finish its work

James 1:4
Let perseverance finish its work so that you may be mature and complete, not lacking anything.

After we are born again, that is the beginning of a new journey. The use of the words "Born again" is so accurate because like babies, we have to learn many things before we can grow up. Along the way there are various stumbling blocks. Some may keep falling more than others and God knows this already. Hence He encourages us to have perseverance and let the Holy Spirit mold us. Of course, our part includes surrendering to the Holy Spirit, but some will mature faster than others. For those who keep stumbling, it is important to realise the need for perseverance and keep coming back to Yshua when we fall. For in Him, there is no condemnation when we confess and repent.