What you probably meant was that anyone obtaining faith and sanctifying grace is part of the faithful. Right?
St. Robert Bellarmine says that God gets Baptism for all his elect.
Scripture attests to this: Romans 8:30 tells us: And whom he predestined, them he also called. And whom he called, them he also justified. And whom he justified, them he also glorified.
So, of those who receive glory, all were predestined, but, they were first called and then justified. This doesn't mean that all who are called are justified, nor that all who are justified are glorified, but rather, from a finished point of view, from heaven's view looking back to the beginnings of those who obtained glory, scripture explains that God called and justified the glorified in heaven. Now, since the promulgation of the gospel, after Christ, those people predestined to heaven obtain Baptism because Christ made it mandatory. For those born prior to Christ, faith alone obtained glory once Christ died and rose and ascended.
Baptism is the distinctive mark of all Christians, and serves to differentiate them from those who have not been cleansed in this purifying stream and who, consequently, are not members of Christ.
Pope Pius XII