Baruch 5:1-9 - Baruch (a prophet) was consoling the Jews of their exile in Babylon
(Letter/Epistle of St Paul to the) Philippians 1:4-6, 8-11 - Thanksgiving
Luke 3:1-6 - Preaching of John the Baptist; encouraging everyone to repent as a preparation for the coming of Jesus
Baruch
He is the scribe and disciple of Jeremiah (prophet). He lived when the Jews were exiled in Babylon.
Background: The Babylonians conquered the Jews around 587 BC. They brought many Jews to Babylon (in present day Iraq). This ended around 538 BC when Cyrus, the Persian conqueror of Babylon, allowed the Jews to return to Jerusalem. Some Jews chose decided to stay in Babylonia.
Philippians
Those who lived in Philippi (in present day Greece).
St Paul, the Apostle to the Gentiles (non-Jews), wrote this letter to the early Church in Philippi, where he established the first Christian community in Europe.
Luke
He was a physician. He was a disciple of St Paul.
He wrote the Gospel of Luke and the Book of Acts (or Acts of the Apostles).
John the Baptist
He is the cousin of Jesus.
His mother is Elizabeth, whom Mary visited. Both were pregnant with their respective sons. (Luke 1:39-45)
He encouraged the Jews to repent. This was marked by the baptism in the Jordan River. He baptism many Jews including Jesus. (Matthew 3:13-17)
Isaiah
Isaiah is one of the prophets in the Old Testament -- around 742 BC to 701 BC, and it may have continued even longer, until 687 BC.
John preaches repentance.