I invite you to read paragraphs 1846 through 1869 in the Catechism. It is available in numerous places on the internet. Paragraph 1857 explains mortal sin in clear language. Paragraph 1865 explains the consequences of "The Proliferation of Sin."
"The Agony in the Garden" is a Sorrowful Mystery of the rosary. Do we really grasp the weight of our sins that Jesus bore?
May this Second Week of Advent bring you God's peace!