The gospel was of first importance to Apostle Paul. Believing the gospel is of first importance to you and me.
“Now I make known to you, brothers and sisters, the gospel which I preached to you, which you also received, in which you also stand, by which you also are saved, if you hold firmly to the word which I preached to you, unless you believed in vain.
For I handed down to you as of first importance what I also received, that Christ died for our sins according to the Scriptures, and that He was buried, and that He was raised on the third day according to the Scriptures, and that He appeared to Cephas, then to the twelve. After that He appeared to more than five hundred brothers and sisters at one time, most of whom remain until now, but some have fallen asleep; then He appeared to James, then to all the apostles; and last of all, as to one untimely born, He appeared to me also (1 Corinthians 15:1-8 NASB).”