Vatican II and the Spiritual Maturity of Priests

Vatican II reiterates what St. Thomas Aquinas taught (Summa Th., 2a2æ.184.6,8), namely, priests, by virtue of their priestly office and ministry, are obliged to a certain spiritual perfection of charity, above and beyond both lay and religious.

Like all other Christians [priests] have received in the sacrament of Baptism the symbol and gift of such a calling and such grace that even in human weakness they can and must seek for perfection, according to the exhortation of Christ: "Be you therefore perfect, as your Heavenly Father is perfect" (Mt 5:48). Priests are bound, however, to acquire that perfection in special fashion. They have been consecrated by God in a new manner at their ordination and made living instruments of Christ the Eternal Priest that they may be able to carry on in time his marvelous work whereby the entire family of man is again made whole by power from above.... 

Holiness does much for priests in carrying on a fruitful ministry. Although divine grace could use unworthy ministers to effect the work of salvation, yet for the most part God chooses, to show forth his wonders, those who are more open to the power and direction of the Holy Spirit [qui, dociliores impulsui et ductui Spiritus Sancti facti], and who can by reason of their close union with Christ and their holiness of life say with St. Paul: "And yet I am alive; or rather, not I; it is Christ that lives in me" (Gal 2:20). [Doesn't this paragraph do away with the so-called "activist" mentality towards apostolate, ministry, and evangelization?] 

Hence, this holy council, to fulfill its pastoral desires of an internal renewal of the Church, of the spread of the Gospel in every land and of a dialogue with the world of today, strongly urges all priests that they strive always for that growth in holiness by which they will become consistently better instruments in the service of the whole People of God, using for this purpose those means which the Church has approved.

(Presbyterorum Ordinis, no. 12; http://www.vatican.va/archive/hist_councils/ii_vatican_council/documents/vat-ii_decree_19651207_presbyterorum-ordinis_en.html)