When did you become a new person? Well, the simple answer is that you became a whole new person when Christ gave you His new life. When Christ entered you and you entered Christ.
But when was that? Some people say that it happened at the cross. When Jesus went to the cross, He accomplished all that was needed for our salvation. He gave His life for you and me on the cross. It is certainly true to say that nothing more than what Jesus did is necessary for our salvation.
The work of our salvation may be entirely on His side, but the relationship is two-way. You entered into a relationship with Jesus willfully and at a certain time in your life. You may not remember exactly when it was and maybe there was a sense in which it was gradual, but there was a time before you were in Christ and there was a time after you became in Christ. He didn’t force you and He didn’t trick you. He wanted a real relationship with you and a relationship is by choice.
So He did all the work, but nothing happened until you wanted Him. Just like a marriage (an illustration the Lord uses), the relationship takes the desire of both sides. He certainly showed us His desire as He made everything ready for us. All He waited for was for us to choose Him. When that happened, we entered into Him and He entered into us. This is all about love.
Not everyone is “in Christ.” Only those who want to be.