You know, I would think it would be difficult, and not knowing any Muslims myself, I am not really qualified to make a testimony on it. However, I do know from Scripture that they are the sons of Ishmael, to whom the God of Abraham also made promises. To the extent they know and worship the God of Abraham, it is possible they may call upon His name.
Saul did not recognize the Lord either, but was a very faithful Jew. When Jesus revealed Himself to Saul, he fell upon His knees. I think this can happen to anyone, no matter how misled they may be by religion.
Paul then went and proclaimed Him to the Athenians, who worshipped Him as “the unknown God”, because they did not know who He was.
I think the book of Galatians would help you make the proper distinction between Issac and Ishmael. So, are you saying Muslims can possibly be saved, even though they reject the heart of Christianity that Jesus was crucified for our sins?
Example of Hagar and Sarah
21 Tell me, you who desire to be under the law, do you not listen to the law? 22 For it is written that Abraham had two sons, one by a slave woman and one by a free woman. 23 But the son of the slave was born according to the flesh, while the son of the free woman was born through promise. 24 Now this may be interpreted allegorically: these women are two covenants. One is from Mount Sinai, bearing children for slavery; she is Hagar. 25 Now Hagar is Mount Sinai in Arabia; [5] she corresponds to the present Jerusalem, for she is in slavery with her children. 26 But the Jerusalem above is free, and she is our mother. 27 For it is written,
“Rejoice, O barren one who does not bear;
break forth and cry aloud, you who are not in labor!
For the children of the desolate one will be more
than those of the one who has a husband.”
28 Now you, [6] brothers, like Isaac, are children of promise. 29 But just as at that time he who was born according to the flesh persecuted him who was born according to the Spirit, so also it is now. 30 But what does the Scripture say? “Cast out the slave woman and her son, for the son of the slave woman shall not inherit with the son of the free woman.” 31 So, brothers, we are not children of the slave but of the free woman. - Gal
By Faith, or by Works of the Law?
3:1 O foolish Galatians! Who has bewitched you? It was before your eyes that Jesus Christ was publicly portrayed as crucified. 2 Let me ask you only this: Did you receive the Spirit by works of the law or by hearing with faith? 3 Are you so foolish? Having begun by the Spirit, are you now being perfected by [1] the flesh? 4 Did you suffer [2] so many things in vain—if indeed it was in vain? 5 Does he who supplies the Spirit to you and works miracles among you do so by works of the law, or by hearing with faith— 6 just as Abraham “believed God, and it was counted to him as righteousness”?
7 Know then that it is those of faith who are the sons of Abraham. 8 And the Scripture, foreseeing that God would justify [3] the Gentiles by faith, preached the gospel beforehand to Abraham, saying, “In you shall all the nations be blessed.” 9 So then, those who are of faith are blessed along with Abraham, the man of faith.
The Righteous Shall Live by Faith
10 For all who rely on works of the law are under a curse; for it is written, “Cursed be everyone who does not abide by all things written in the Book of the Law, and do them.” 11 Now it is evident that no one is justified before God by the law, for “The righteous shall live by faith.” [4] 12 But the law is not of faith, rather “The one who does them shall live by them.” 13 Christ redeemed us from the curse of the law by becoming a curse for us—for it is written, “Cursed is everyone who is hanged on a tree”— 14 so that in Christ Jesus the blessing of Abraham might come to the Gentiles, so that we might receive the promised Spirit [5] through faith.
The Law and the Promise
15 To give a human example, brothers: [6] even with a man-made covenant, no one annuls it or adds to it once it has been ratified. 16 Now the promises were made to Abraham and to his offspring. It does not say, “And to offsprings,” referring to many, but referring to one, “And to your offspring,” who is Christ. 17 This is what I mean: the law, which came 430 years afterward, does not annul a covenant previously ratified by God, so as to make the promise void. 18 For if the inheritance comes by the law, it no longer comes by promise; but God gave it to Abraham by a promise.
19 Why then the law? It was added because of transgressions, until the offspring should come to whom the promise had been made, and it was put in place through angels by an intermediary. 20 Now an intermediary implies more than one, but God is one.
21 Is the law then contrary to the promises of God? Certainly not! For if a law had been given that could give life, then righteousness would indeed be by the law. 22 But the Scripture imprisoned everything under sin, so that the promise by faith in Jesus Christ might be given to those who believe.
23 Now before faith came, we were held captive under the law, imprisoned until the coming faith would be revealed. 24 So then, the law was our guardian until Christ came, in order that we might be justified by faith. 25 But now that faith has come, we are no longer under a guardian, 26 for in Christ Jesus you are all sons of God, through faith. 27 For as many of you as were baptized into Christ have put on Christ. 28 There is neither Jew nor Greek, there is neither slave [7] nor free, there is no male and female, for you are all one in Christ Jesus. 29 And if you are Christ’s, then you are Abraham’s offspring, heirs according to promise.
We are to proclaim Him, the head of the church. It seems many Catholics rather proclaim the body instead of the head.
