While salvation through Jesus' sacrifice is surely the focal point of the Gospel, sanctification is one of the most under-discussed miracles of God's completed work on the cross. When Jesus died on the cross and declared "it is finished", He not only opened the gates of heaven to us, He also revealed the stairway to sanctification.
So what is sanctification? When we look at the Latin word 'sanctus' it means to be set apart to be used for a holy purpose; does this ring a bell? 1 Peter 2:9 "But you are a chosen generation, a royal priesthood, a holy nation, His own special people, that you may proclaim the praises of Him who called you out of darkness into His marvelous light". This is exactly what sanctification does - once you accept Jesus as your personal Lord and Savior, you are given a royal status by the most powerful, one and only creator of the universe! He calls you by name (Isaiah 43:1) and has set you apart from the rest of creation as His own child, part of His inheritance in the Kingdom of heaven after these few decades on earth. The perfect verse to put this all into perspective is 2 Corinthians 5:17 - "Therefore, if anyone is in Christ, he is a new creation; old things have passed away; behold, all things have become new."
You are truly BORN AGAIN, not in the flesh but of the Spirit (read John 3, Jesus and Nicodemus) and with this new Spirit living in your heart, you will start to despise sin when it calls out to you. Now don't get me wrong, we do not become sinless, we just start to sin less - and this is only thanks to the new attitude, outlook and priorities that have been formed in us by the Holy Spirit; this is our sanctus, our calling to be used for a holy purpose!
So the next time you feel like God doesn't want to use you, think again. God has a purpose and plan for everyone - we just need to start realizing that we are precious to God; why else would He go through all that trouble of the cross? Do check out the post on our purpose in life under the "Inspiring Questions" page to really tie this together.