Came in beside (παρεισηλθεν). Second aorist active indicative of double compound παρεισερχομα, late verb, in N.T. only here and Galatians 2:4 which see. See also εισηλθενin verse Romans 5:12. The Mosaic law came into this state of things, in between Adam and Christ.

That the trespass might abound (ινα πλεοναση το παραπτωμα). It is usual to explain ινα here as final, as God's ultimate purpose. So Denney who refers to Galatians 3:19; Romans 7:7. But Chrysostom explains ινα here as εκβασις (result). This is a proper use of ινα in the Koine as we have seen. If we take it so here, the meaning is "so that the trespass abounded" (aorist active subjunctive of πλεονασω, late verb, see on 2 Thessalonians 1:3; 2 Corinthians 8:15). This was the actual effect of the Mosaic law for the Jews, the necessary result of all prohibitions.

Did abound more exceedingly (υπερεπερισσευσεν). First aorist active indicative of υπερπερισσευω. Late verb, in N.T. only here and 2 Corinthians 7:4 which see. A strong word. If πλεοναζω is comparative (πλεον) περισσευω is superlative (Lightfoot) and then υπερπερισσευω goes the superlative one better. See υπερπλεοναζω in 1 Timothy 1:14. The flood of grace surpassed the flood of sin, great as that was (and is).