The Gospel of Luke (in The Bible, of course) is the first half of the writing by Luke, a physician; the Book of Acts is the second half of his writing. The book of Luke is the third of four gospels, and it is the one which begins with the births of the cousins, John the Baptist and Jesus. The narrative soon gets to Jesus's teaching, and this particular account of Jesus's life concentrates heavily on Jesus's teachings about social justice.
Just a word about the fact that the gospels do not all tell exactly the same story. Each of the writers of the gospels records the life and words of Jesus through the lens of his own concerns. That does not create chaos for readers; instead, it reveals the heart of the writer. Think of it this way: we all take different points or lessons away from any teaching, despite the fact that we heard the same message. That does not negate the message, but it does say something about us as listeners. No doubt this is why Jesus shared his message in many ways during His three years of ministry.
Social justice, of course, is how we are to treat the least among us: the poor, the sick, and the needy. In short, those who cannot care for themselves. The best example of this comes from the passage of scripture known informally as "the beatitudes." This is a series of blessings Jesus conferred on those who probably need it most. Luke 6:21 says:
"Blessed are ye that hunger now: for ye shall be filled."
In contrast, Matthew 5:6 says it this way:
"Blessed are those who hunger and thirst for righteousness, for they will be filled."
Notice that Luke's statement is a practical application of blessing--literal food for the hungry--while Matthew's version is more about sustenance for the soul.
While Matthew lists a total of nine beatitudes, Luke presents only four of them. Then he adds four stern warnings to those in society who do have material things, something not found in Matthew. Verses 24-26 read as follows:
But woe unto you that are rich! for ye have received your consolation. Woe unto you that are full! for ye shall hunger. Woe unto you that laugh now! for ye shall mourn and weep. Woe unto you, when all men shall speak well of you! for so did their fathers to the false prophets.
These admonitions are spoken by Jesus to those who have means; He is reminding them that they, too, could be in need one day.
Several other instances of social awareness and justice are found only in Luke's gospel. For example, the familiar story of the Good Samaritan is in Luke, and it is the quintessential story of social justice. Luke also recounts several stories about Jesus which are not found in the other three gospels about women and which particularly champion charity toward widows. Jesus tells those who have come to hear Him speak that they are to give their coats away if they have more than one and see someone in need (3:11), give something to anyone who begs from them (6:30), and lend even (perhaps especially) to those who cannot give anything in return (6:34). In Luke chapter 7, Jesus also accepts a woman everyone else avoids because she is a sinner.
The Gospel of Luke clearly presents Jesus as a champion for social justice.