The tax collector and Pharisee

Luke
I find the parable of the Pharisee and the tax collector (see Luke 18:9-14) almost similar to the parable of the lost son.  The Pharisee is sort of close to God, in that he is always trying to do his duty and pray and all that, but he really doesn't understand God at all.  The tax collector has little regard for the law, has previously abandoned God, but realizes his need for God and repents from the depths of his heart.  He desires to get back to God.  The Pharisee is like the older brother in the parable of the lost son, and the tax collector is like the son who ran away from home.
The tax collector, as Jesus points out, is the one who God really listens to.  That doesn't mean that if you haven't committed terrible sins, God won't listen to you.  The point here is that we have to approach God with sincerity of heart and in humility.  That was the prayer of the tax collector, and that should be our prayer too.

Breaking the Sabbath

Key verse
Romans 5:19 - For just as through the disobedience of the one man the many were made sinners, so also through the obedience of the one man the many will be made righteous.


Numbers/Matthew
I would have liked more information about the man who broke the Sabbath (see Numbers 15:32-36).  He was gathering wood on the Sabbath, and those who found him brought him to Moses and Aaron, and he was stoned to death outside the camp, on God's orders.  Was it because he didn't trust God to provide the wood after the Sabbath, or he hadn't thought of God's day the day before, so he was had to gather wood on the Sabbath?  The story doesn't offer many details, and I'm left hoping that God didn't just have him stoned out of an unintentional sin.  But here is where we have to go on faith that God is gracious and compassionate and has proven himself to be such time and again.
In some ways, it is easy to see how the Pharisees became so focused on the letter of the law (see Matthew 23:23).   Looking at stories like this one from Numbers could lead them to think that breaking the Sabbath by doing any work is completely out of the question, or else you'll suffer the consequences.  But Jesus had the right attitude - it's not the outward appearance, but what's going on in the heart that God really looks at, so that is what we must focus on.

The sign of Jonah

Key verses

Psalm 36:5-6 - Your love, O Lord, reaches to the heavens, your faithfulness to the skies.  Your righteousness is like the mighty mountains, your justice like the great deep.

Matthew

Jesus was talking to the Pharisees and Sadducees, people who knew the law inside and out and yet didn't follow the heart of God's message.  Perhaps this is what Jesus was getting at when he said that their generation would only receive the sign of Jonah.  "A wicked and adulterous generation looks for a miraculous sign, but none will be given it except the sign of Jonah."  These are just my thoughts, but I'm thinking the sign of Jonah is that, just like Jonah heard God's message but didn't fully accept it, so these people hear what Jesus is saying, but aren't accepting his message.  Instead of the Jews accepting Jesus, the Gentiles will hear and repent, just like the Ninevites did.

More righteous than the Pharisees

Matthew
Matthew 5:20 can be confusing unless one digs a little deeper.  The text says: "For I tell you that unless your righteousness surpasses that of the Pharisees and the teachers of the law, you will certainly not enter the kingdom of heaven."  How can our righteousness surpass the Pharisees?  They're experts in following the law. 
The catch is, Christ came to fulfill the law (as mentioned just previously to verse 20).  We can't have a righteousness of our own just by following the law, because we can't keep the whole law.  Fortunately, through Christ, who has fulfilled the whole law, we can obtain righteousness greater than that of the Pharisees.  Faith alone will get us there, not any works that we could do ourselves.  Thus, through Christ, we can enter the kingdom of heaven!