Have you ever felt that something in your past is affecting what's happening to you today? Perhaps you have had difficulty making friends, or getting good grades in school, so it seems impossible to think that something good can happen to you in a certain area; there seems to be no precedent for it. Or even if you have overcome a difficulty, maybe the memory of it is still negatively affecting your outlook on things. Such thoughts can sometimes convince us to not take advantage of an opportunity, or to give up on something because of a preconceived notion that there is little chance of succeeding. Christian Science, however, reveals that these thoughts are not legitimate or God-sent but are aggressive mental suggestions, having no true substance. God's thoughts are always good, and there's no weakness, no point of vulnerability, in our real being as God's image. Since man reflects God, Spirit, man is actually spiritual and has no mortal history—good or bad—to overcome. Realizing this can help us right now, in practical ways.
I've found reassurance from an experience of St. Paul's in the Bible. See Acts 28:1-6. He was being taken as a prisoner to Rome by the Romans and was shipwrecked on an island with other prisoners and Roman soldiers. The natives of the island were kind and lighted a fire because it was cold and had begun to rain. While Paul was putting sticks on the fire, a poisonous viper appeared and fastened itself on his hand. The natives concluded that this man must be a murderer and was now going to die for his past sins. But Paul shook the serpent off without hesitation, and to everyone's astonishment he did not die or even suffer any ill effects from the snakebite.
To me, what is impressive about this account is the swiftness with which Paul did away with the serpent. Before he had converted to Christianity, he had been a zealous persecutor of Christians. Had Paul been receptive to the suggestion that he deserved to die for what he had done in the past, perhaps he would not have been able to shake the serpent off so quickly. But he knew that a knowledge of the love of God and of man's relation to Him enables us to destroy all evil. Paul's real identity was not in a material body or human history at all but was spiritual and immutable, and he was able to prove this, even if everyone around him accepted an incorrect view of him. Sin does have to be repented of and destroyed, but once destroyed, we do not have to suffer for it. Sin is not part of man's true history or identity.
