God is love (1 John 4:16) and He created mankind in order to express His love towards us (We are an expression of His love).

As to what gives us purpose in life, I suppose there are many different things (our families, our jobs etc.), however, for a Christian, I suppose they are quite similar. For me, it's having a personal relationship with God. It's God loving me enough to be involved in my life and allowing me to be involved in His life. It's also being able to share God's love with others and spending time with my family.

I know this life is very short in the overall scheme of things. Only knowing that when this life is over I will be with the Lord in heaven makes it possible to go on. I cannot imagine living this life without the Lord. He gives me peace and purpose in the present and hope for the future.