God is the sovereign power and authority over all of creation and beyond. In order to exist within creation, you have to have a relationship with God. Without God, nothing exists. Without a relationship with God, you cannot exist within the realm of God. Therefore, you need some mechanism for establishing a relationship with God in order to live eternally with Him. Without that relationship, you will live in an existence without God, which we commonly call the Lake of Fire. Therefore, salvation is required in order to establish a relationship with God.
When you were born into this world, you are born physically alive and spiritually dead.
As such, you were born under the master of sin, and without a relationship with God.
When you were born, Adams original sin was imputed genetically into your body. And though you cannot be condemned because of someone else’s sin, namely Adam, however, as you grew up and became accountable for your thoughts and actions, your personal sins made you accountable to sin, which sealed the foundation for your eternal condemnation.
Being condemned, and needing a relationship with God, you had only two options.
First, you can try to correct your situation yourself, and somehow gain Gods approval and acceptance.
Second, you could let God correct your situation, and believe in His work, and therefore gain Gods approval and acceptance.
Under the first option, you would have to live a perfect life. Moses wrote down all of the perfect life requirements, with all of the thou shalt not’s, and, if you could fulfill all of these requirements, then you would be perfect, as God is perfect, and therefore would have an automatic relationship with God, at His level.
However, sin is the master, and no one is capable of living their own perfect life. Therefore, under sin, and not being able to live the perfect life, you are condemned.
Under the second option, all of the work is placed in Gods hands. God came up with a plan, wherein the second person of the Trinity, who has the title Son of God, and who we know as Jesus Christ, was born into this world as a man, lived the perfect life, accepted upon Himself, the punishment for the sins of all of humanity, and in effect provided us with a solution to our eternal predicament.
Having done this work, God gave us the gift of salvation, wherein all we have to do is believe in Christ and His work, and therefore possess the salvation that is necessary to have a relationship with God, and simultaneously obtain eternal life.
Faith in Christ, sets us free from the bondage of sin.
Being free from sin, we are no longer under the stringent requirements of sin. In other words, we are not obligated to live a perfect life in order to obtain salvation, which none of us can do anyway.
By faith, we are no longer slaves of sin, we are now servants of righteousness. Righteousness being that perfect life that we no longer have to work for, because Gods righteousness was given to us as a gift when we believed in Christ.
Under the law of sin, you are expected to live the perfect life, which is typically called human works.
Under the law of Christ, you are expected to live by grace, which is Gods favor, which is Gods gift.
Mans works are not a part of the law of Christ. God did all of the work, and God receives all of the credit. We receive the benefit of that work, by means of faith, not from our own works.