Well I didn't know this about J.I. Packer...

I'll end with a personal illustration from J. I. Packer's life that shows how crucial it is that we not get off balance here with either extreme and begin to say either that there is no holiness necessary or that perfection is possible in this age. (Packer teaches theology at Regent College in Vancouver.)

I've heard him tell the story in person, and I've read it in two different books. In 1944 he was studying Latin and Greek in Corpus Christi College, Oxford, and playing in a jazz band called "Oxford Bandits." One evening he attended a meeting of the Christian Union and heard a sermon from a relatively unknown preacher named Earl Langston. He said, "The scales fell from my eyes . . . and I saw the way in."

But soon came the crisis. There was a good bit of false teaching around Oxford, especially regarding perfectionism and the possibility of a second experience of "sanctification by faith" - by which they meant a crisis experience after which you wouldn't have any more struggle with sin, which is not what I mean by that term! Packer had a very sensitive conscience and could not deceive himself. He was not perfect and no matter how many times he reconsecrated himself to God there was still no perfection. He said it could easily have led him to suicide if it were not for two great discoveries: the writings of John Owen on indwelling sin (especially volumes 6 and 7 of his Works) and the writings of J. C. Ryle (especially his book on Holiness). Here he learned the Biblical realism of "indwelling sin" and the ongoing fight of faith and the glorious rest that comes from God's righteousness imputed to us in Christ by faith alone.

https://www.desiringgod.org/messages/who-is-this-divided-man-part-2

As a Christian, there will always be a disconnect between who we should be and how we should behave or view the world, and from the reality of how we feel and behave. It is a fundamental fact that we wont be perfectly sanctified in this life. Look to Paul in Philippians 3 or JI Packer’s testimony or John Owen’s books (it is interesting, John Wesley championed Christian Perfectionism, but he himself didn’t even attain it if his later writings would suggest, though him not knowing God is most likely self-depreciation). Still, this doesn't mean we give up or stop striving to be holy/godly. We still must run to the Cross, mortify our indwelling sin, and ask God to strengthen us through humbling/breaking us. The reality of the Gospel in our life should naturally/supernaturally lead us to do missions, love others, produce fruit/good works, and make disciples.

More references: https://en.wikipedia.org/wiki/Christian_perfection