Despite being the father of lies, not everything Satan says is a lie. In fact, some of the most effective lies are those that contain the right amount of truth to appear wholly true. One of the few truths Satan will tell you? You're not good enough for God, there are things in your past, present, and even your future that you ought to be ashamed of, and you absolutely deserve God's wrath.
But let me tell you, my brethren, this is a glorious truth! While we are not to sin so that grace may abound (Roman 6:1-2), when we inevitably do sin, grace does abound. Every thing in your life about which you ought to be ashamed is just one more reason you ought not be ashamed of the Gospel!
Are you a sinner? Yes. Let no pride sink deep enough into your heart that you mistakenly believe you lack sin. Through His Apostle John, God tells us that to spout such rubbish is to deceive ourselves (1 John 1:8). But are you saved? Have your sins been nailed to the cross? Are you washed in the blood of the Lamb? Rejoice! For nothing you have ever done, nothing you could possibly do, can overpower His love and grace (Romans 8:35-39).
Consider Paul. How many of us even know such a man? A man who killed Christians just for being Christians. Paul knew the error of his past ways, and often thought back on it with remorse. Was he worthy to be an Apostle? In his own words, no! This man, who named himself chief of sinners (1 Timothy 1:15), nevertheless received and rejoiced in his role as God's messenger.
If God can do this with Paul, what can He do with you? Whoever you are, whatever your past, your future is bright in Christ, the light of the world. He dwells within you, and so will your life not reflect that? And will He not fulfil His promises? Laugh in Satan's face. The taunts he throws at you are out of jealousy and anger, because while you are destined for Heaven, he will be the most pathetic prisoner of Hell. He wants you to feel chained because he will be chained. He wants to suffocate you because he knows his final desperate gasp is approaching. The rage inside this creature shall never die, but praise be to God, neither will those who believe in the Lord.
Recommended song: Are You Washed in the Blood of the Lamb? - Alan Jackson