Jesus charged us to go into all the world and preach the gospel. He said He would be with us always. He also said that the gates of hell will not prevail against His church. He not only believed the church could be successful, He actually commanded the church to go and be successful.
I am reminded of the situation in the wilderness when Israel was told to go and take the land. After sending spies into the land, the people demonstrated a lack of trust in God. It was not the first such demonstration, but it was the straw that broke the camel’s back. When they disregarded God’s charge and listened to the “evil report” of the ten spies rather than the good report of the two, God disinherited them and took their children instead (40 years later). What did God expect them to do when they saw the giants that made them look like grasshoppers in their own sight? What did God expect them to do when they heard of the great walled (fortified) cities? He expected them to trust Him. He told them He would be with them. He had shown them that He would be with them.