A.T. Robertson Commentary Romans 5:15

"But not as the trespass, so also [is] the free gift. For if by the trespass of the one the many died, much more did the grace of God, and the gift by the grace of the one man, Jesus Christ, abound unto the many." — Romans 5:15 (ASV)

But not as the trespass (αλλ' ουχ ως). It is more contrast than parallel: "the trespass" (το παραπτωμα, the slip, fall to one side) over against the free gift (το χαρισμα, of grace χαρις).

Much more (πολλω μαλλον). Another a fortiori argument. Why so? As a God of love he delights

much more in showing mercy and pardon than in giving just punishment (Lightfoot). The gift surpasses the sin. It is not necessary to Paul's argument to make "the many" in each case correspond, one relates to Adam, the other to Christ.