What is God's requirement for salvation (GRFS)?
Foundationally having a belief there is God (Rom1):
NKJ 1 Corinthians 3:11 For no other foundation can anyone lay than that which is laid, which is Jesus Christ (Jesus is the Christ)
NKJ 2 Timothy 2:19 Nevertheless the solid foundation of God stands, having this seal: "The Lord knows those who are His," and "Let everyone who names the name of Christ depart from
iniquity unrighteousness."
In Acts13:16-41 we have a record of Paul evangelizing to Jews and God-fearing Gentiles. To make it clear what Paul means by "Christ" in Acts13:33 he references Psalm2. In Ps2 "YHWH's Messiah/Christ/Anointed" is YHWH's King who He has made King of kings to who He gives the earth as His inheritance. When we read "Christ" in the NT Writings we should automatically recall Ps2 to understand and explain what Christ means and who Jesus is. With this in mind it's pretty simple to use some basic logic and common sense to understand that belief that Jesus is the Christ the Son of God (also referenced in Ps2:7 and Acts13:33) the King of kings must include bowing the knee to Him in faithful obedience (which is Paul's self-described mission to the nations in Rom1:5 & 16:26). We can also see Paul being wholly absorbed with the message (or compelled by the Spirit depending on Greek manuscripts) to proclaim to the Jews that Jesus is the Christ.
The last clause in 2Tim2:19 stated as part of God's solid foundation and seal is a command to all of those who are "The Lord's" to depart/withdraw from/distance yourselves from/revolt from (apostatise from) unrighteousness (which is sin 1John5:17 and lawlessness 1John3:4 which the Lord hates Heb1:9).
The above Foundation is commanded by God in 1John3:23: Believe in the name of God's Son Jesus Christ and love one another as He commands.
Foundationally the message is pretty simple: Believe as commanded by God that Jesus is the Christ/King and live out your days in submission to His Absolute Rulership. And this lasting belief and lasting submission are biblically one and the same thing.