Acquittal and life for all followed upon Christ's perfect obedience. Law ... to increase the trespass, this is explained in 7:7-13.
Romans 7:7-13: The law & sin. Though the law is holy ... and good, it not only makes man conscious of sin (Galatians 3:19), but also incites to sin (coveteousness; compare Exodus 20:17; Deuteronomy 5:21). Probably a reminiscence of a thoughtless, carefree boyhood brought to an end (death) by the dawning sense of moral obligation & guilt. The real enemy is sin, which uses even what is good (the law) to make a man more sinful than he would otherwise be.
Reference summary used from The New Oxford Annotated Bible with Apocrypha Expanded Edition, An Ecumenical Study Bible, RSV