I believe that Paul was addressing everyone who had attended. Both Jews & Gentiles alike. I also believe there were unbelievers in the crowd.
What is Grace?
Grace is God’s unmerited favor to ill-deserving sinners in Jesus Christ. The presence of the risen Christ, extending God’s forgiveness and power so that God’s provision of His Son for redemption is effected through the agency of the Holy Spirit in the heart of man.
Grace is eternal (II Tim. 1:9), immutable (Rom. 11:29), sovereign (Rom. 9:11-24), effectual (Eph. 2:8-9; John 6:37, 39, 44, 63-65), and destroys all room for human boasting (I Cor. 1:29-31; 4:7). It means that the Triune God gets all the praise, honor, and glory for our salvation: The Father for planning it, the Son for purchasing it, and the Holy Spirit for applying and uniting us to it (Eph. 1:2-14). Christ is not only efficient, but is alone sufficient for salvation (Heb 9:12; 10:10) such that our own merit or works righteousness can do nothing to either attain or maintain our justification. The assistance of grace does not even depend on the humility or obedience of man ... for it is a gift of grace itself that we are obedient and humble ...as the Apostle says, "What have you that you did not receive?" (1 Cor. 4:7), and, "But by the grace of God I am what I am" (1 Cor. 15:10). Faith is, therefore, not a product of our unregenerated human nature (John 1:13, 6:63-65; Rom 9:16) but is exercised as the infallible result of the work of the Holy Spirit opening our eyes and ears to the beauty of the gospel, turning our heart of stone to a heart of flesh and uniting us to Christ.
Monergism.com
There is no human boasting or claims we can make it in earning or meriting it. And this pertains to both Jew & Gentile alike.
Romans 3:21
For there is no distinction:
23for
all have sinned and fall short of the glory of God,
24and are justified by his grace as a gift, through the redemption that is in Christ Jesus,
By Grace Through Faith
1And you were dead in the trespasses and sins
2in which you once walked, following the course of this world, following the prince of the power of the air, the spirit that is now at work in the sons of disobedience—
3among whom we all once lived in the passions of our flesh, carrying out the desires of the body
a and the mind, and were by nature children of wrath, like the rest of mankind.
4But
c God, being rich in mercy, because of the great love with which he loved us,
5even when we were dead in our trespasses, made us alive together with Christ—by grace you have been saved—
6and raised us up with him and seated us with him in the heavenly places in Christ Jesus,
7so that in the coming ages he might show the immeasurable riches of his grace in kindness toward us in Christ Jesus.
8For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,
9not a result of works, so that no one may boast.
10For we are his workmanship, created in Christ Jesus for good works, which God prepared beforehand, that we should walk in them.
One in Christ
11Therefore remember that at one time you Gentiles in the flesh, called “the uncircumcision” by what is called the circumcision, which is made in the flesh by hands—
12remember that you were at that time separated from Christ, alienated from the commonwealth of Israel and strangers to the covenants of promise, having no hope and without God in the world.
Paul is making it clear that there is no distinction: for all have sinned and fallen short. Paul says we are all in the same boat.
Hope this helps. If I come off too direct, please let me know. I am dealing with a lot of pain, so please bear with me. I apologize in advance if I do.
God Bless!
In Christ, Our Justification, Our Sanctification, and Our Redemption 1 Cor. 1:30