First Nephi 18:3
This verse is a cause-and-effect phrase - The Lord showed him great things because he went to the mount often, and he prayed often. The mount could also symbolize the temple. It is notable that Nephi continued to seek the Lord and His knowledge - the "great things" that Nephi was shown was surely included more than how to build the ship. The Lord wouldn't have shown Nephi great things unless Nephi had returned to the mount oft, and prayed oft unto the Lord.