"I have been crucified with Christ; and it is no longer I that live, but Christ living in me: and that life which I now live in the flesh I live in faith, the faith which is in the Son of God, who loved me, and gave himself up for me." (ASV)
This is a crucial point to the Christian walk, yet one which more often than not we forget. It's easy for us to say "I've prayed and God's forgiven me, so now I'm done and I'm going to heaven" but that's not all that Christ desires of us. It doesn't end with that first prayer. "And he called unto him the multitude with his disciples, and said unto them, If any man would come after me, let him deny himself, and take up his cross, and follow me." (Mark 8:34 ASV) We cannot follow Christ and still live our lives the way we did before. We have to become His.
Christians do all kinds of things to proclaim to the world that they love God. Anyone remember those WWJD bracelets that were so popular a few years ago? There are bumper stickers, t-shirts, and any number of other marketable items that proclaim the name of God. We go to church on Sunday. We hang scripture verses on our walls at home. We volunteer. We do good things. None of this is ultimately wrong, but it is not proof of salvation either. No bumper sticker is a ticket into Heaven. We all know hypocrites who attend church regularly but don't really believe in God. Christ never said if you want to follow Me, buy the merchandise.
God expects our devotion to Him to be much deeper than any of these things. He expects us to know Him and He wants to know us. "Many will say to me in that day, Lord, Lord, did we not prophesy by thy name, and by thy name cast out demons, and by thy name do many mighty works? And then will I profess unto them, I never knew you: depart from me, ye that work iniquity." (Matthew 7:22-23 ASV) Christ wants to be the most integral part of our life. He wants to live in us so that once our bodies die, we can live in Him.