This is about the perfection in Christ.....on a purity level. On that level one has the mind of Christ...but not the maturity that goes along with withstanding all the wiles of the devil. That takes experience...and having come through trials and tribulations.The spiritually mature are not to consider that they have attained brother. That is very clear and very simply said in that scripture. And if anyone is truly mature (perfect) that is the mind they will have, since that is the mind that would be indicative of their maturity.
There is no half-perfection of Christ..... or half mind of Christ...or half holiness. There is a partial maturity...which is called immaturity.
An apple is fully an apple in its immature state. A newborn baby is fully a human being.
The difference is that a newborn in the Spirit can only grow into a spiritual maturity by going to get the full measure of grace. Otherwise all we get are mature people but without the spiritual dimension. We can only grow up to be something according to our environment.
Why don't we have orange trees in the arctic? The environment is wrong...not conducive to the life of that tree.
Why can't we just grow up into Christ with one initial downpayment of grace? (and this is important) Because without the dimension of the Spirit that we BUY with all we have ....we only form a character that is temporal in nature. Without the crossing over into the spiritual realm, on judgment day our works will burn up as they are not pure. Without being crucified in the outer man we grow in the outer man religious part of us along with the inner man of faith...and the weeds choke out the wheat...so that no fruit is permitted to grow. That is unless we are crucified and made to walk in the heavenly dimension IN Christ.
When our weeds are taken away, the wheat is free to grow. When we are crucified with Christ the inner man can be joined to God in Christ and bear a spiritual and eternal fruit.
Once one understands how the kingdom realm is entered into and walked in...then we will see that the flesh is just in the way and needs to be pulled out by the roots. Go to the cross...