How can I discern whether or not someone is a Christian? Do they have shiny faces? Do they love others more than the average person? Do they talk about God all the time? Do they behave differently than most?
I suppose all of these could be true, but the Bible gives only one test of being “in the faith” or being a true follower of Jesus Christ.
Examine yourselves, to see whether you are in the faith. Test yourselves. Or do you not realize this about yourselves, that Jesus Christ is in you?—unless indeed you fail to meet the test! (2 Corinthians 13:5)
Notice first that the test is not for other people. We might think we can figure them out, but who can be certain about the heart of anyone else? Instead, we are to examine ourselves. And the test is simple: does Jesus Christ live in me? If not, then I fail the test.
Salvation is not about what I do or do not do. It is not about whether I attend church or not, or if I give to the poor or not. Even though these could be the evidence of Christ being in my life, others who do not have Him could do these things too. The test is about Jesus.
The Bible talks about this as a mystery once hidden, but now revealed to the people of God. Again, we understand that our salvation is not about our performance, but…
this mystery once hidden for ages and generations but now revealed to his saints. To them God chose to make known how great among the Gentiles are the riches of the glory of this mystery, which is Christ in you, the hope of glory. (Colossians 1:26–27)
With Jesus, I have new life. He is my life. Sin ruins and separates me from God, but Jesus and the life of Jesus changes everything. He makes me alive, forever.
But if Christ is in you, although the body is dead because of sin, the Spirit is life because of righteousness. (Romans 8:10)
Having the life of Christ in me is a matter of faith. That is, Jesus said, “Truly, truly, I say to you, whoever believes has eternal life” (John 6:47). But that life is in and of Christ, nothing else.
And this is the testimony, that God gave us eternal life, and this life is in his Son. Whoever has the Son has life; whoever does not have the Son of God does not have life. I write these things to you who believe in the name of the Son of God that you may know that you have eternal life. (1 John 5:11–13)
Because of Jesus, I pass the test. I have eternal life. It is not based on who I am or what I do, but on Him, the one who died for my sin and now lives for my redemption. Eternal life is all about Jesus who lives forever and who makes Himself available to all who are willing to receive Him.
But to all who did receive him, who believed in his name, he gave the right to become children of God, who were born, not of blood nor of the will of the flesh nor of the will of man, but of God. (John 1:12–13)