A man was not created to die. However, through Adam sin (NOT sins plural, but sin singular) entered the world. Through sin entered death.
God stated the man’s problem from that point on like that “to-die you-shall-die” in Hebrew (usually translated “you shall surely die”, which misses the point: death is both a process and a final destination). So sinis the force that drives the process of destruction, corruption – i.e., death as a process, which leads to death as a finality.
When people think about the word “sin”, they think about the sin nature acted out, or acted upon. Those are the outworkings of sin, usually called “sins” (plural, since they take several forms, depending on the context in which the sin nature is acted out). The entire book of Romans of Romans mention “sin” (singular, meaning sin as a principle or force) well over 40 times (including derived words like “sinful”), and the word “sins” meaning “acts of sin” only 3 times! If you read the first 8 chapters of Romans through this lense, they will make perfect sense. The issue is the sin force / nature, which generates acts of sin (sins) and which end in death.
During Old Testament times, Mosaic law was given to serve as a litmus test. Just as a test strip turns a certain color to indicate the presence of a certain substance, so did the law of Moses – it caught outworkings of sin, or sins, to indicate the presence of sin substance. The litmus test’s only value is to point to the presence of a certain substance – it has no power over that substance. Same with the law of Moses – it has no power to eliminate sin and give life, but it points to the presence of the substance of sin, and to the need of having life.
Again, I must emphasize this – don’t think “sins” in plural as in “criminal acts deserving of punishment” in this context, think of “sin” in singular as “a substance that infects, weakens, and degenerates anything that it comes in contact with”.
The universe is very complex and well-tuned on both on macro and micro levels. Everything in creation testifies to a creator – take for instance, the engineering complexity of DNA with all the information it carries, all the error-correcting mechanisms it possesses, etc. Yet at the same time the entire universe is moving toward chaos. How can it be – all that observed perfection, yet at the same time everything moves toward chaos? This state of affairs is only possible in one scenario – everything was created perfect, and after that a corrupting force was introduced in creation. The Bible presents this principle / force as “sin”. I believe that the principle of entropy (which is attested to, for one, by the 2nd law of thermodynamics) is a very good definition of how sin works in the world.
So you see how sin as a force drives the things it infects to chaos, destruction, disintegration – i.e., to death. If anything keeps on being disintegrated – it’s only a matter of time until there’s nothing left of it. While that destructive force is at play, nothing can be eternal. If a human is infected with sin – eternal life isn’t possible for him by definition.
In the Bible, it’s called “the law of sin and death”.
Now, when people receive Jesus, they receive eternal life:
24 “Most assuredly, I say to you, he who hears My word and believes in Him who sent Me has everlasting life, and shall not come into judgment, but has passed from death into life.
Here’s the mechanism whereby eternal life “works”:
2 For the law of the spirit of life in Christ Jesus has made me free from the law of sin and death.
Our new born-again spirit doesn’t have sin as a force / nature in it. Therefore, the new law (as in “law of physics”, not as in “criminal law”) of spirit that has life canceled out the law of sin that produces death. That’s why we are called on to “live by the spirit” – because the born-again spirit part of out being has no sin. If we live by the spirit – we release life and God’s perfection. That life can be released and will “give life to our mortal bodies”. That new awesome and fun way of living is called “holy life”, or “life of wholeness”!