When we hear the word "Christian" we assume that they are the only ones who believe in Jesus as the Messiah. In fact, there are many Christians who do not believe in Jesus as the Messiah, have difficulty with the concept of his virgin birth, and definitely do not believe that he is scheduled to return to the earth to commence a millennial reign as King. In contrast, there are many Jews, Muslims and members of other religions who believe emphatically that Jesus is their Messiah, and is scheduled to reign as King over the earth for one thousand years. The Christians who have similar beliefs are often referred to as fundamentalists.
The question then becomes whether members of other religions need to become "Christians" if they claim Jesus as their Messiah. The short answer is "no." Not everyone who considers themself a Christian is a disciple of Jesus, and certainly, not every "Christian" will have a place in God's kingdom. The more appropriate terminology is discipleship. To Jews who had believed in his message, Jesus said, "If you hold to my teaching, you are really my disciples. Then you will know the truth, and the truth will set you free" (John 8:31-32). Thus, holding to the teachings of Jesus is pivotal not only to our understanding of his message of redemption, but also, to our having a place in his kingdom.
The core of Jesus' message is that we should avoid sexual immorality, impurity, debauchery, idolatry, witchcraft, and drunkenness, and pursue love, joy, peace, patience and self-control. When we understand the consequences for violating spiritual law, being a disciple of Jesus becomes the only viable option. Let the God of Israel, El Shaddai, be praised.