You ought to make every effort to free yourselves even from venial sin, and to do what is most perfect.- St. Teresa of AvilaSt. Teresa is the first great Teresa of the Carmelite saints and blesseds. As far as I know, they are named in religious life in honor of her...
Anyways, St. Teresa's works are The Interior Castle and The Way of Perfection. From the titles one can see that the Doctor of the Church was deeply devoted to perfecting her interior life at the expense of worldliness in a complete dedication to Jesus Christ. She was a mystic, famously represented in Bernini's Saint Teresa in Ecstasy.
Our Lord tells us in Matthew to seek first the Kingdom. In Luke, he instructs us, that if we wish to follow him, that "let him take up his cross and follow Me." Our cross is first and foremost that of sin. We were born into sin and ignorance, and while original sin is removed from us at baptism, the consequences are not. Concupiscence, or the desire for things contrary to reason and goodness, remains. But grace is given abundantly so we can conquer the effects of sin and enter into union with God in Heaven.
We must accept our personal sins and work to eliminate them. Then we must work to eliminate our failings that are small, not so much sins but imperfections. Things Jesus wouldn't think and think to do. But we only can achieve this through grace! So frequent the sacraments! Blessed John Paul apparently confessed daily. There are reasons why that's good for him, being the Pope under attack from the devil all the time is one, and not for us, but he's more than any of us living people are, being a blessed of the Church and all.
As to the mysticism: No mystic is not first an ascetic, one who denies himself those things of the flesh and the world and gives them up for Our Lord. We all need to be ascetical according to our own abilities and vocations.
We're not going to be perfect in this life. We need to seek perfection though as God is perfect. Part of this is recognizing that Christ on the cross conquered sin, death, and Satan through love. "Love is patient..." The virtue of faith, acquired when grace spurs the will into accepting God as seen through Revelation, leads us to hope in the life to come, which leads us to charity, which abides forever.