Grace alone by faith alone expressed in love for God and man - the one and only true gospel.
You've been given opportunity after opportunity to present the gospel that Paul preached as the power of God, and for whatever reason, you cannot or will not answer. The preaching of the cross is the power of God (1 Corinthians 1:18 KJV)/the WHY of the cross (1 Corinthians 15:1-4 KJV); that Christ died for our sins and that He was buried and rose again the third day is the good news by which we are saved!
1 Corinthians 15:1
Moreover, brethren, I declare unto you the gospel which I preached unto you, which also ye have received, and wherein ye stand;
1 Corinthians 15:2
By which also ye are saved, if ye keep in memory what I preached unto you, unless ye have believed in vain.
1 Corinthians 15:3
For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures;
1 Corinthians 15:4
And that he was buried, and that he rose again the third day according to the scriptures:
And yes, our salvation is by grace through faith!
Ephesians 2:8 For by grace are ye saved through faith; and that not of yourselves: it is the gift of God:
Ephesians 2:9 Not of works, lest any man should boast.
but it hasn't always been/will be that way for all people of all time!
While it's true that all salvation, Genesis through Revelation, requires faith; not all salvation in the Bible is/will be by grace through faith (Ephesians 2:8-9 KJV). James wrote James 2:18 KJV, James 2:20 KJV and James 2:24 KJV.
Many (future) will go through the trial of their faith: receiving the end of their faith, even the salvation of their souls. Of which salvation the prophets enquired and searched diligently, who prophesied of the grace that should come unto them (notice too, that it is of the grace that should come unto them).
1 Peter 1:7-10 KJV
That is NOT the same as trusting the Lord's faith and finished work in our place believing 1 Corinthians 15:1-4 KJV. It's a done deal! We didn't DO anything for it Ephesians 2:4-9 KJV, Titus 3:4-7 KJV!