1Jo 5:13 These things have I written unto you that believe on the name of the Son of God; that ye may know that ye have eternal life, and that ye may believe on the name of the Son of God.
As you can see, your church is lying to you...You can KNOW you have eternal life (salvation) from the scripture, alone...
Joh 20:30 And many other signs truly did Jesus in the presence of his disciples, which are not written in this book:
Joh 20:31 But these are written, that ye might believe that Jesus is the Christ, the Son of God; and that believing ye might have life through his name.
Everything that is needed for salvation is written in the scripture and it is verified by the very scripture you need to study...
Neither 1 John 5 or John 20 say that.
1 John 5 (and many other similar passages) state that the faith is Christ is necessary for salvation. John 20:31 adds to that that the Gospel of John is written to aid in that beleif. Neither passage says that the scripture is sufficient alone. In fact both passages say that it is faith and not the written word that is necessary, but even as regards faith the passages do not say that it is sufficient, and in fact we know from other scripture that it is not.