Our greatest calling in life is the calling Jesus gives to those who choose to follow him. In Matthew 4:19, Jesus says to Simon Peter and Andrew "Come, follow me, and I will make you fishers of men."
As fishermen, they used nets to catch fish. As followers of Jesus Christ, the Law and the Gospel are the nets we use to catch men. We don't want anyone to swim past these nets and into the gates of hell. We want to prevent as many people as possible from going anywhere near those gates.