Essentially, there are ultimately two classes of people: the elect, and the reprobate. But both of these categories are conceived in sin, and are initially in complete and utter rebellion against God, His Christ, His church, and everything related to the Messiah's kingdom expansion.
But what is sometimes not understood--and which really should be--is that there *are* some "sub-categories" under these two main paradigms.
One of them is that of the already-redeemed, (those who are indeed already born again, and who have the new nature of Jesus in them).
Another is that of the formidable reprobate: those who will never be regenerated, and who are happy to go to hell. (We are not in a position to determine that any particular human being is in this class. Only God can do that.)
A third category is that of those on whom the Holy Spirit is working, (and who yet will not, in the end, be converted). These people are, at least for a time, willing to sincerely hear the word of the gospel of grace.
A fourth category, (and this is the main theme of this post), is that of the yet-unconverted, but soon-to-be converted souls. These people are, by the grace of God, in (as it were) the church's "spiritual womb." People from all nations, cultures, religious backgrounds, and ethnicities are found in this class.
What is the upshot of all this? Simply this: that it is not fair to assume that a Muslim (to use one example) is, by virtue of the fact that he is a Muslim, necessarily completely dead-set against the things of Christ. If he is in the "womb," he will, in God's good time, come to faith in the true God, and be united to the true church.