Because of Who He said He was; He said He was God. In John 8:58, Jesus said, "Truly, Truly, I say to you, before Abraham was, I AM." When He said, "I AM," He was quoting from the Old Testament in Exodus 3:14. That is where Moses was talking to God, and asked Him His name. God answered and said, "I AM." When Jesus said "I AM," He was claiming the name of God for Himself, and thereby claiming to be God. Other great men of history point to a philosophy and teach good ideas. Only Jesus pointed to Himself, claimed to be God, and spoke with authority that matched His claim.
Because of what He did; Jesus forgave sins (Luke 5:20). He rose from the dead (Luke 24; John 2:19-21), raised others from the dead (John 11:43-44), and He walked on water (John 6:19). No one on earth has ever done the things Jesus did. There is no way around it- Jesus is special; about that, there can be no doubt.