1 Corinthians 2:12–13 (KJV 1900)
12 Now we have received, not the spirit of the world, but the spirit which is of God; that we might know the things that are freely given to us of God. 13 Which things also we speak, not in the words which man’s wisdom teacheth, but which the Holy Ghost teacheth; comparing spiritual things with spiritual.
How do we know we can be saved; that is, those of us who are not Jews and are not God’s chosen People? It is because of the mystery that has been received. We did not learn it from the spirit of the world (cosmos). There is no universal wisdom which can save a man. Our revelation of the mystery (which is: there would come a period of grace for all men, Jew and Greek) is only by the spirit which is of God, that has been revealed.
When the spirit of God reveals his truth to us through his revealed word (and it was first announced by Paul) we understand that our salvation is by grace (it is no longer a mystery), though we are Gentiles, and is freely given to us of God. The Corinthians were depending on human wisdom: “I am of Paul; and I of Apollos; and I of Cephas…”
Now the things that were once a mystery or secret can be openly announced by us. Comparing spiritual things with spiritual. This can only be accomplished through studying the Bible, which is whay Paul admonished us to:
“Study to show yourself approved unto God, a workman that needeth not be ashamed, rightly dividing the word of truth.” 2 Timothy 2:15
Everything about our faith hinges on the Bible. Without it, the people are useless.