Barna and other researchers continue to conclude that Christianity is shrinking not just within the US but globally. But, this cannot be in a biblical sense.
In John 6, Jesus says, “37 All that the Father gives me will come to me, and whoever comes to me I will never cast out. 38 For I have come down from heaven, not to do my own will but the will of him who sent me. 39 And this is the will of him who sent me, that I should lose nothing of all that he has given me, but raise it up on the last day. 40 For this is the will of my Father, that everyone who looks on the Son and believes in him should have eternal life, and I will raise him up on the last day.” (ESV)
We are not seeing Christianity decreasing. We are seeing the elect of God distinguishing themselves from the world. Those who once called themselves believers (just as the crowd earlier in John 6 would have said) have been revealed as having never knew God in the first place.
What we are seeing today is no different than what we see in verses 63-66.
” 63 It is the Spirit who gives life; the flesh is no help at all. The words that I have spoken to you are spirit and life. 64 But there are some of you who do not believe.” (For Jesus knew from the beginning who those were who did not believe, and who it was who would betray him.) 65 And he said, “This is why I told you that no one can come to me unless it is granted him by the Father.”
66 After this many of his disciples turned back and no longer walked with him.” (ESV)
Jesus is calling his people out from among world. So when we see those “falling away”, don’t lose heart. Instead, rejoice that Christ is calling His people to Himself.
So what shall we say then, as believers who haven’t “left the faith?”
” 67 So Jesus said to the Twelve, “Do you want to go away as well?” 68 Simon Peter answered him, “Lord, to whom shall we go? You have the words of eternal life, 69 and we have believed, and have come to know, that you are the Holy One of God.” -John 6:67-69 (ESV)