One must be saved before they can believe the Gospel of their Salvation !
Eph 1:13
In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were sealed with that holy Spirit of promise,
One had to be saved in the first place to spiritually hear the word of truth, then faith or believing follows.
In fact, Paul places being saved before calling by the Gospel in the purpose of God here 2 Tim 1:9
9 Who hath saved us, and called us with an holy calling, not according to our works, but according to his own purpose and grace, which was given us in Christ Jesus before the world began,
Notice the order, hath first saved us, then called us [by the Gospel] with an holy calling. We are called by the Gospel after we are saved 2 Thess 2:13-14
13 But we are bound to give thanks alway to God for you, brethren beloved of the Lord, because God hath from the beginning chosen you to salvation through sanctification of the Spirit and belief of the truth:
14 Whereunto he called you by our gospel, to the obtaining of the glory of our Lord Jesus Christ. 30