Today is the feast of St. Tomasso d'Aquino, Doctor of the Church. From his commentary on the book of Colossians, on Colossians 1:3-6:
Our good consists principally in faith, hope, and charity; for through faith we have familiarity with God, through hope we are raised up to Him, but by charity we are united to Him. I Cor. XIII, 13: 'so now abide faith, hope, and charity, these three', &c. And so he [St. Paul] gives thanks for these three. First, that they [the Colossian Christians] have faith, although he was not the one who preached to them, which was a disciple named Epaphras, and later Archippus. Thus he says 'hearing of [your] faith', which is the source of spiritual life. Hab. II, 4: 'my just one lives from faith'. Hebr. XI, 6: 'who would draw near to God should believe', &c.
But this faith without working love is dead, as is said in Iac. II, 17. And thus it ought to be that there is a working love. Gal. ult.: 'in Christ Jesus, neither circumcision nor foreskin is worth anything, but a new creation'. And so he says, 'and the love which you have, etc.'.
For there is a love of charity and a worldly one, but the worldly one does not extend itself to all, because love is to those with whom there is communion, which is the cause of love, and this cause in worldly love does not pertain to all, but only to those who share blood or who share worldliness, but the love of charity extends itself to all. And thus he says 'in all'. For even if sinners are loved, this is so that at some point they might be saints. 1 Io. III, 14: 'we know that we are translated from death to life, because we love the brethren'.
Moreover, the world's love has fruit in this world, but charity has it in eternal life. And this third he puts under hope, saying, 'according to the hope that is laid up', that is, according to eternal glory, which is called hope, because it is held as certain. Iob XIX, 27: 'laid up is my hope in my heart'.
[Super ad Colossenses, sect. 11, my translation]
If you want to read St. Thomas without getting too heavily into technical matters, I recommend the commentary on Colossians very highly; I think it's one of the best commentaries on Colossians ever written and it is a fairly good introduction to important elements of St. Thomas's theology, but it is also relatively short and readable.
