St. Thomas Aquinas was a 13th century Dominican friar, theologian and philosopher. His most famous work is the Summa Theologica from which these readings are taken. The Second Vatican Council said that scholarly investigations should be done especially following the example of St. Thomas. The Catholic tradition considers St. Thomas's ideas very important, but of course he is not held to be infallible. If you would like more information on St. Thomas, please see the article in the Catholic Encyclopedia on him.
The organization of each article in the Summa Theologica may be confusing at first. First we get several "Objections". These are views and arguments that St. Thomas is opposed to--they argue for the very opposite of the conclusion he wants to establish. Don't misread the objections for views of St. Thomas! Next we get a section labeled "On the Contrary". Here St. Thomas cites some eminent authority, often a Church Father or a Biblical text, in favor of the view he wants to defend. The main part of the text is next, starting with "I answer that", which gives St. Thomas's own view and his arguments, both theological and philosophical, for this view. Finally, we get "Replies to Objections" where St. Thomas critically responds to the initial objections. You may want to print out this rough guide to the text.
The readings are below. Please read them all. All the readings are from the Summa Theologica, and are referred to by the part number, question number, and article number.
Remember two things. St. Thomas thinks charity is a special kind of love of human beings for God, and he thinks this kind of love is a gift of God.