"...charge some that they teach no other doctrine, nor give heed to fables and endless genealogies, which cause disputes rather than godly edification which is in faith. Now the purpose of the commandment is love from a pure heart, from a good conscience, and from sincere faith, from which some, having strayed, have turned aside to idle talk, desiring to be teachers of the law, understanding neither what they say nor the things which they affirm." -Paul (1 Timothy 1:3-7)
By the reading above, you can see that the purpose of the message of Jesus is love. It also gives details, "Love from a pure heart, from a good conscience, and from sincere faith." Sometimes we lose track of this and become focused on how much we know. Other times it is all about who we know. Still, other times we are more concerned about our image. If you keep reading it continues to discuss that some have turned aside from the main purpose of the message (love), and have become more focused on teaching the law even though they don't understand what they are saying.
Why can we so easily forget why we do what we do?
Many of us are more focused on making ourselves look good, than we are accomplishing a task for God. I can remember watching certain pastors, and other leaders, and becoming impressed by their teaching, clothes, style, and jokes. I would try to incorporate some of the things that I saw into my life. It's great to learn from others, but it's not great to try to be them. At times, I became more focused on them than I was on God. I admit, I was wrong. If you try to be someone else, you subtract who God made you to be off of this earth. Surely all of us get sucked in to this method of thinking at one time or another, but that doesn't mean it is acceptable.
So, to answer the real question, "Why do we spread this message?" Love. Pure, sincere, and genuine love. It's simple.