1. Corinths 15: 1-4

Now I make known unto you brethren, the gospel which I preached unto you, which also ye received, wherein also ye stand,

2 by which also ye are saved, if ye hold fast the word which I preached unto you, except ye believed in vain.

3 For I delivered unto you first of all that which also I received: that Christ died for our sins according to the scriptures;

4 and that he was buried; and that he hath been raised on the third day according to the scriptures;


This passage of Paul is great. It teaches us:
1. You can believe in vain
2. The gospel is not only about the cross but about
resurrection too! Without a belief in the resurrection, you are
NOT a christian


vain
http://strongsnumbers.com/greek/1500.htm
greek: without cause or reason, vainly
eikḗ – properly, without cause (ground), without basis and therefore not to be taken seriously (considered valid). This adverb suggests, "What goes to no purpose . . . ".

So people who have actually fallen after
they have believed in Jesus CAN fall
but this is because they have believed in vain, have
had a belief without fruit and commitment
one that was simply not rooted in the heart but in vain.

THis does not at all stand in contrast to Romans 8:38-39
For I am persuaded, that neither death, nor life, nor angels, nor principalities, nor things present, nor things to come, nor powers,

39 nor height, nor depth, nor any other creature, shall be able to separate us from the love of God, which is in Christ Jesus our Lord.