Feast of St. Luke the Evangelist

It is said that the Christians of Antioch were once under siege from Turks, and defeat seemed inevitable. In their dire straits they turned to God and prayed; and it is said that when they did some in the church saw a man in shining garments praying with them. He said his name was Luke, and that he, too, was of Antioch, and that in remembrance of the many saints and martyrs given to heaven by Antioch, the Lord had allowed them to assist the people of the city in their time of need. Taking heart, the Christians of Antioch forced the lifting of the siege and put the Turks to rout.

Here is the opening of the Sermon on the Plain, one of the most famous sections of the Gospel attributed to Luke:

Looking at his disciples, he said:

Blessed are you who are poor, for yours is the kingdom of God.
Blessed are you who hunger now, for you will be satisfied.
Blessed are you who weep now, for you will laugh.
Blessed are you when men hate you, when they exclude you and insult you and reject your name as evil, because of the Son of Man. Rejoice in that day and leap for joy, because great is your reward in heaven. For that is how their fathers treated the prophets.

But woe to you who are rich, for you have already received your comfort.
Woe to you who are well fed now, for you will go hungry.
Woe to you who laugh now, for you will mourn and weep.
Woe to you when all men speak well of you, for that is how their fathers treated the false prophets.

But I tell you who hear me: Love your enemies, do good to those who hate you, bless those who curse you, pray for those who mistreat you. If someone strikes you on one cheek, turn to him the other also. If someone takes your cloak, do not stop him from taking your tunic. Give to everyone who asks you, and if anyone takes what belongs to you, do not demand it back. Do to others as you would have them do to you.

If you love those who love you, what credit is that to you? Even sinners love those who love them. And if you do good to those who are good to you, what credit is that to you? Even sinners do that. And if you lend to those from whom you expect repayment, what credit is that to you? Even sinners lend to sinners, expecting to be repaid in full. But love your enemies, do good to them, and lend to them without expecting to get anything back. Then your reward will be great, and you will be sons of the Most High, because he is kind to the ungrateful and wicked. Be merciful, just as your Father is merciful.

One of the neatest resources on the Gospel of Luke, at least for theological purposes, is Thomas Aquinas's Catena Aurea on the Gospels. You can find it here. I also recommend Cyril of Alexandria's Commentary on Luke.