Please add spaces between words: IfyoubelieveinChristtodayandhaveeternallife,butloseittomorrow,thenitwasnever"eternal"atall.Henceifyouloseyoursalvation,thepromisesofeternallifeintheBiblewouldbeinerror.
If you believe in Christ today and have eternal life, but lose it tomorrow, then it was never "eternal" at all. Hence if you lose your salvation, the promises of eternal life in the Bible would be in error.