I've been told God knows if I am going to heaven or to hell before
I've been born. Does that mean that it doesn't matter what I do in my
life ...good or bad...that I will go to heaven or hell anyways??
Let's say a friend of mine is walking down the street, and sees a five dollar bill fall from someone's pocket. What will he do? If this is a good friend and I know him/her fairly well, I have a very good idea as to whether or not the money will be returned to the rightful owner or kept. I know this, because of the way this person has handled other situations, but I am not 100% positive of the outcome.
Now if I can make pretty accurate predictions, with my limited knowledge, how much more can God, who is ALL KNOWING? I might know how your mind works, but God knows the heart. This is not to say that you have no free will, because you do. We always have the freedom to make our own choices. When I am able to say, "I know that person, the five dollars will be returned," does not mean that the five has to be returned. That choice still has to be made by the person themselves.
God knows each human heart, and knows how they will respond. this does not mean to say that I can live my life without care or worry, because God wants all people to be in heaven. That is why He continues to guide us, sometimes with little nudges, sometimes with bigger ones.
To say that the outcome is already set, and I can live my life any way I want, means we have no free will. Besides, God already knows who has decided that course, and may not have included him/her in the book of life.