The Guilt of the First Sin is So Great that It Can Be Washed Away Only in the Blood of the Mediator, Jesus Christ
Nevertheless, that one sin, admitted into a place where such perfect happiness reigned, was of so heinous a character, that in one man the whole human race was originally, and as one may say, radically, condemned; and it cannot be pardoned and blotted out except through the one Mediator between God and men, the man Christ Jesus, who only has had power to be so born as not to need a second birth.
Source: The Enchiridion (New Advent)