The scriptures read are Obadiah, Psalm 116 and Matthew 18.
Obadiah. We've heard before about the enmity of Israel (descended from Jacob) and Edom (descended from his brother Esau). Obadiah is prophesying against Edom for the culmination of that rivalry, some great injustice done to Judah when it was already down. This is probably the fall of Jerusalem to the Babylonians.
In v. 15, Edom is told that what they did will be done to them. Or as people say today, karma. God's judgment is just.
Psalm 116. A heartfelt version of this psalm.
Matthew 18. Children may be loved but they are the most powerless members of society. Jesus is turning the earthly idea of greatness upside down.
The "little ones" in the rest of the passage are probably child-like believers, not necessarily actual children. Leading one astray is condemned by Jesus in the strongest possible terms. The millstone referred to is literally a "donkey's millstone."
We must be ruthless about the stuff that diverts us from following Jesus, even if it feels like it is a part of us.
V. 10 is the origin of the idea of guardian angels.
Jesus gives great advice for dealing with problems in the church. Keep involvement to the smallest number of people possible; don't make it a matter for the whole church unless you can't solve it between yourself and the person who sinned against you (yes, sinned not just annoyed or rubbed you the wrong way.)
Jesus says a lot of good stuff here about forgiveness. The parable of the merciless servant echoes what Obadiah says in verse 15 above.