well I agree it is the gospel of Christ and not another that secures salvation for all who believe (meaning in truth)
your op does not exactly read that way though. as you can see, you are getting varied answers
your bio also states 'not Christian' so what do you believe then?
I believe the gospel Paul recieved from Christ. 1 Corinthians 15:3,4.
That has to be believed by anyone who hears the gospel to have 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,
If they do not believe this gospel alone for salvation God's words says they will end up before the judgement seat still in their sins.
Or if Christ comes and they are alive, He will come in flaming fire punishing those who know not God and do not obey the gospel of Christ. To obey the gospel God requires us to believe it.
2Co_5:10 For we must all appear before the judgment seat of Christ; that every one may receive the things done in his body, according to that he hath done, whether it be good or bad.
2Th 1:8 In flaming fire taking vengeance on them that know not God, and that obey not the gospel of our Lord Jesus Christ:
2Th 1:9 Who shall be punished with everlasting destruction from the presence of the Lord, and from the glory of his power;