Experiencing signs and wonders does not ensure salvation. Despite being healed by Jesus, the paralytic man at the pool of Bethesda chose to reject the Lord and align himself with the Jews.
When evangelizing to the lost world, Christians must be prepared to provide a reasoned defense of their faith in response to the objections of unbelievers. This is the essence of Christian Apologetics.
Jesus was warmly welcomed by the people of Sychar. They listened to His words and believed Him to be the Messiah. However, because a prophet is often without honor in his own country, the people in Judea and Galilee struggled to believe in Him, even when His teachings were accompanied by signs and wonders.
After her encounter with Jesus, the Samaritan woman at the well eagerly shared the news about the Messiah. Her testimony led many Samaritans to believe in Jesus and to receive Salvation for their souls. This story exemplifies the blessings that are both given and received through Evangelism.