Objection 1. It would seem that charity cannot be perfect in this life. For this would have been the case with the apostles before all others. Yet it was not so, since the Apostle says (Philippians 3:12): "Not as though I had already attained, or were already perfect." Therefore charity cannot be perfect in this life.
Objection 2. Further, Augustine says (Qq. lxxxiii, qu. 36) that "whatever kindles charity quenches cupidity, but where charity is perfect, cupidity is done away altogether." But this cannot be in this world, wherein it is impossible to live without sin, according to 1 John 1:8: "If we say that we have no sin, we deceive ourselves." Now all sin arises from some inordinate cupidity. Therefore charity cannot be perfect in this life.
Objection 3. Further, what is already perfect cannot be perfected any more.
But in this life charity can always increase, as stated above (Article 7). Therefore charity cannot be perfect in this life.
On the contrary, Augustine says (In prim. canon. Joan. Tract. v) "Charity is perfected by being strengthened; and when it has been brought to perfection, it exclaims, 'I desire to be dissolved and to be with Christ.'" Now this is possible in this life, as in the case of Paul. Therefore charity can be perfect in this life.
I answer that, The perfection of charity may be understood in two ways: first with regard to the object loved, secondly with regard to the person who loves. With regard to the object loved, charity is perfect, if the object be loved as much as it is lovable. Now God is as lovable as He is good, and His goodness is infinite, wherefore He is infinitely lovable.
But no creature can love Him infinitely since all created power is finite. Consequently no creature's charity can be perfect in this way; the charity of God alone can, whereby He loves Himself.
On the part of the person who loves, charity is perfect, when he loves as much as he can. This happens in three ways. First, so that a man's whole heart is always actually borne towards God: this is the perfection of the charity of heaven, and is not possible in this life, wherein, by reason of the weakness of human life, it is impossible to think always actually of God, and to be moved by love towards Him. Secondly, so that man makes an earnest endeavor to give his time to God and Divine things, while scorning other things except in so far as the needs of the present life demand. This is the perfection of charity that is possible to a wayfarer; but is not common to all who have charity. Thirdly, so that a man gives his whole heart to God habitually, viz. by neither thinking nor desiring anything contrary to the love of God; and this perfection is common to all who have charity.
Reply to Objection 1. The Apostle denies that he has the perfection of heaven, wherefore a gloss on the same passage says that "he was a perfect wayfarer, but had not yet achieved the perfection to which the way leads."
Reply to Objection 2. This is said on account of venial sins, which are contrary, not to the habit, but to the act of charity: hence they are incompatible, not with the perfection of the way, but with that of heaven.
Reply to Objection 3. The perfection of the way is not perfection simply, wherefore it can always increase.
Source: Summa Theologica (New Advent)