It is impossible to be a Christian without the Holy Spirit. This is one reason Jesus told His disciples, "I tell you the truth: It is for your good that I am going away. Unless I go away, the Counselor will not come to you; but if I go, I will send Him to you." (John 16:7)
God the Father sent His Son to save us because He loves us. The Son of God suffered and died on the cross for our sins. And the Holy Spirit brings people into a relationship with our Creator through faith in Christ. He comes to live inside everyone who believes in Jesus as Savior.
So is God's Spirit in everyone? Well, we find the answer to that question in Scripture.