Numbers 21:7 Therefore the people came to Moses, and said, We have sinned, for we have spoken against the Lord, and against thee; pray unto the Lord, that he take away the serpents from us. And Moses prayed for the people.
God had sent poisonous serpents among the people, and many died. This experience led them to confess their sin. The serpent punishment worked as God intended. They asked Moses to pray for them that He would take away the serpents. And Moses responded to the penitence of the people by praying for them. Moses became the intercessor, the mediator, that we all need.
Presumably, Moses prayed what they asked him to: to take away the serpents. The Lord did not take away the serpents. Serpents represent Sin; the deadly poison is the effect of sin. So it is in our lives: God does not take away the presence of sin from among us. Instead, He gives us His Son on the cross (the serpent on a pole): so that whoever believes in Him (looks upon Him) will not perish, but have eternal life. The lesson is clear: Believe in Jesus and live! (John 3).
The Lord will not take us away from the presence of sin until we die and live with Him. But He will take away the penalty of sin now: eternal life today. The bronze serpent takes our sin upon himself. “The Lord has laid on the iniquity of us all.” “For our sake He made Him to be sin who knew no sin, so that in him we might become the righteousness of God [1 Corinthians 5:21].”
See in this story what mighty things prayer will do.