Reading the Old Testament we can see that the word “sin” is referred simply to the "violation of the law"; and this disobedience of the law leads to punishment by God's justice. While reading the New Testament we see Jesus Christ the incarnated Word of God came to our world to reveal for us the love of God and the destiny which he created man for, which is man’s participation in His glory. God has set as the destiny of all people; participation in His Glory, and of His divine love. “All have sinned and fall short of the glory of God” (Romans 3: 23). God has set this as our destiny and in Christ He has made it clearly possible for us to attain it. Because of Christ Who, as true human, arrived at this destiny and attained to it for all mankind, we can inherit it by choosing to strive for a life in Christ . “Grace and peace be multiplied to you in the knowledge of God and of Jesus our Lord, as His divine power has given to us all things that pertain to life and godliness, through the knowledge of Him who called us by glory and virtue, by which have been given to us exceedingly great and precious promises, that through these you may be partakers of the divine nature, having escaped the [c]corruption that is in the world through lust.”( 1peter1:1-5)
According to the New Testament the word “sin” in the Greek language in which it was written is “amartia” which means “ to go off the goal” or “to miss the mark”. The New Testament was very clear in defining the word “sin”. Sin is missing the mark and the goal of our lives as Christians. What is our goal as Christians according to the New Testament?. Our Goal is to live in unity with God the Father through His Son Jesus Christ. To be in His likeness. To receive and accept Jesus in us in the Holy Spirit.
Basing our actions in our lives on the divine life of our Lord and Savior Jesus Christ. Therefore, when we “go off the goal” we sin.
Since the goal for which man was created is full communion with God, to partake of the Divine Nature (2 Peter 1:4), sharing in His glory and immortality, then sin means to fall short of the destiny of participation in God. St. Paul expresses this concept of sin when he says that "all have sinned and fallen short of the glory of God" (Romans 3:23) that is, "everyone has missed the mark and fallen short of the goal of man's destiny, which is to participate in the glory of God”.
"Sins" are those things we do which reveal obviously our separation from God; and make us fall short of our goal. All sins are mortal, because all sins separate us from the source of immortality, Who is God. Then to have a faith in God means to choose freely and truly to submit your will to the will of God and to be in unity with Him.
God created the world pure and free from evil. The appearance of moral evil and the suffering of human race are the consequences of sin; which entered our life. Evil entered the world as a consequence of the fall, which occurred, according to the word of God, originally in the world of fleshless spirits, and then in the human race ( Fr. Michael Pomazansky).
God does not punish man for his sins and sinfulness in this life, or even in the life to come. But we are the ones who forged our destiny. We are the ones who have chosen the ways of the devil which led us to death. Death is both cause and result of missing the goal of the immortality which results from the union with God. So death is not a punishment of God: it is, rather, the result of man's failure to live up to his destiny of participating in God's immortality. Death is the primary manifestation of separation and alienation from God; it is also our main source of bondage, “ Inasmuch then as the children have partaken of flesh and blood, He Himself likewise shared in the same, that through death He might destroy him who had the power of death, that is, the devil, 15 and release those who through fear of death were all their lifetime subject to bondage. “ (Hebrews 2: 14-15) and the driving force behind individual sins. Saint Paul said, "Even so we, when we were children, were in bondage under the elements of the world" (Galatians 4:3).
Sins are all those things which form a barrier between us and participation in God. We also refer to these things as "lusts." If we read the New Testament carefully and see that "the Kingdom of God is within you" and "you are the temple of the Holy Spirit," we learn that the origin of sin is really this: we choose to build in our hearts the principality of this world rather than the kingdom of God. The struggle against sin can really be defined as man's role in building a new kingdom within himself, as Saint Paul says: "Are ye not aware that to Whom ye yield yourselves to obey as servants, ye are truly His servants Whom ye obey: whether of sin unto death, or of obedience [to God] unto righteousness?" (Romans 6:16).
The authority of this world rules in a man's heart. He chooses to conquer that principality and replace it with the indwelling of Jesus Christ . He knows that with the help of the Holy Spirit it can be done. Such a person then becomes a warrior of God's Kingdom. He begins to train for battle, he enters a spiritual warfare learning how to fight and struggle against this principality of death within himself. In this war, which is fought in one's own conscience, mind and soul, we must choose to defeat and conquer one of the enemy's strongholds and attain our goal. We must make the choice to have Christ’ dominion over our heart. When we take this decision and accept Jesus to dwell in us, He comes with his healing power that releases us from the bondage of sin and gives us His victorious power over all the thoughts and deeds of lust, hatred, greediness, immorality, malice, fornication..etc. He makes us new in His holiness. So He came to change our nature by giving us His overcoming nature over sin and death.