Jesus 1st followers, weren't an organized religion...
they were just followers of Christ that acknowledged his shed blood on the cross as their ultimate sacrificial "once & for all", "it is finished" Lamb sacrifice to pay for their sins.
The term "Christian" came into play because Jesus Followers "Followed his example"
in so doing, non-believers called them "Christ-likes" cause they acted like Jesus Christ.
So anyone (even Catholics) that receive Jesus shed blood as a free gift payment for the atonement for there sin, can be a saved Christian testified by fruits of the spirit that follow showing repentance has taken place, "love, Joy, peace, patients, long suffering, caring for one another & others even more than themselves. vs "works of the Flesh" Gal. 5,19