Romans 5:15 :

But the free gift isn’t like the trespass. 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 to the many.

It’s pretty easy for us to understand how a small thing can contaminate a big thing. One fly can spoil a whole cup of water. It’s more challenging for us to understand how a single
person can save all of mankind.

Adam, being only one man, brought sin to the rest of his family. This is not that difficult to understand because we know that we inherit things from our parents. The gift of God is
also passed down from a single man: Jesus Christ.

God’s grace or unmerited favor, is more powerful than sin in that the thing that Jesus passes down overrides the thing that Adam passed down. There is very real victory over our sin by
trusting in the grace of God through Jesus.

So, unlike a poison that spoils a glass of water, Jesus work is more like a purification process that makes the water pure. His work is more powerful than poison in our lives. We don’t have to be the same person that we used to be. When we become Christians, God changes us to be pure like Jesus and this spreads to anyone who will have faith in Him.