Love God and love others are definitely tenets of Jesus's teaching. His job on earth was to further the will of his father. God's goal is that our time on earth should further his will and expand his heavenly kingdom. With that respect, don't forget that Jesus also expected his followers to do just that. "Go ye therefore and be fishers of men." His followers were to continue his teachings after he ascended to heaven.
What an excellent answer to outline the parables. I'll go with the first half of your question, then. It seems to me the elemental message of Jesus while He was here on earth was two simple things: Love God and love others. That's really the gist of all his teachings. Some were designed to help us love God more, and some were reminders that we're to love those around us. Consider the story of the Good Samaritan. Here's a case where a man did both--because he loved God, he took exceptional care of a stranger on the road--someone who was his natural enemy and had been beaten up by others. Love God and love others. It's a simple message, but so difficult to live out at times.
This is a very broad question - which I'm going to attempt to give a focused answer to. I think there are several ways this could be answered however, and I hope other editors contribute further thoughts.
Through many parables Jesus addresses several different aspects of the kingdom of Heaven. Here are a few that have more examples than what I have listed:
- It will grow from something very small into something very great: "The Parable of the Mustard Seed and the Yeast" (Matthew 13 or Mark 4)
- It is something far more valuable and precious than anything on earth: "The Parable of the Hidden Treasure and the Pearl" (Matthew 13); "Treasures in Heaven" (Matthew 6)
- There will be a very clear separation between those who will enter and those who will not: "The Parable of the Net" (Matthew 13); "The Parable of the Sower" (Luke 8); "The Rich Young Man" (Matthew 19); "The Parable of the Weeds" (Matthew 13)
- Those who did not accept Jesus' teachings and do not enter the Kingdom will one day regret it: "The Rich Man and Lazarus" (Luke 16)