Thematic Bible: Why the law was given

So then, just as [God's] judgment came, condemning all people [to physical death] because of one sin [i.e., Adam's]; even so the free gift of being made right with God and [resulting in] life may be received by all people because of one man's [i.e., Christ's] act of righteousness. [Note: This "life" may refer to spiritual life now, or to being made alive in the resurrection, which would reverse the curse of physical death caused by Adam's sin]. For just as many people [i.e., all mankind] were considered [by God] to be sinners [and thus to suffer physical death] through the disobedience of the one man [i.e., Adam]; even so, many people [i.e., all believing mankind] will be considered right with God [and thus live again] through the obedience of the one man [i.e., Christ]. Now the law of Moses was introduced [into the world] in order to cause sin to increase [i.e., it defined many things to be wrong that were previously not regarded as sin]. But with the increase of sin, God's unearned favor increased all the more. read more.
This was so that just as sin ruled [over mankind], causing [physical] death, even so God's unearned favor would rule [over mankind], providing [them with] righteousness, and leading to never ending life through Jesus Christ our Lord.