There is much speculation and debate about what actually took place at the Cross.

To the best of my understanding, here are four vital and distinct things that happened at Calvary.

1) Redemption from the transgressions that were under the first testament.

The NT book of Hebrews (probably penned by Paul) was written to Jews, and it contains this little nugget; Heb 9:15 … Christ is the mediator of the new testament, that by means of death, for the redemption of the transgressions that were under the first testament, they which are called might receive the promise of eternal inheritance. So the first thing achieved at Calvary was redemption from the transgressions that were under the first testament.

(2) Reversal of the imputation of sin to all humanity into the imputation of righteousness to all humanity.

Romans 5:18 states “Therefore as by the offence of one judgment came upon all men to condemnation; even so by the righteousness of one the free gift came upon all men unto justification of life.”
Antagonists of this claim use a number of arguments to refute what is perfectly clear in the Bible they claim is inerrant.
(a) The greek word ALL in the first part of this verse is not equivalent to the word ALL in the second part of this verse. The weak minded fallacy of this is seen in that (i) Both words are precisely the same word in the original greek text, and (ii) it is also the same word used earlier in Romans when Paul says that ALL have sinned and come short of the Glory of God. These charlatans would have their cake and eat it too.
(b) IF Adam by his action placed all humanity under sin and Christ by His action made only a FEW people righteous, then we can draw no other conclusion than Adam was far more effective than Christ; or to put it another way Christ was far weaker than Adam.
So the second thing achieved at Calvary was to replace the imputation of sin upon all humanity into the imputation of righteousness upon all humanity.

(3) The third distinct thing that was achieved at Calvary, was the genesis of a brand new, never before seen, completely New Creation.

KJVA 17 Therefore if any man be in Christ, he is a new creature: old things are passed away; behold, all things are become new. The word “creature” in the original greek text, means ‘species’. As the last of the ADAM species, or as the Bible puts it, the Last Adam, died, all humanity was placed in the body of Christ and born again into a completely new species.

There we have it;
(1) Redemption from the transgressions that were under the first testament.
(2) Reversal of the imputation of sin to all humanity into the imputation of righteousness to all humanity.
(3) The genesis of a brand new, never before seen, completely New Creation.