For if the dead are not raised, not even Christ has been raised; and if Christ has not been raised, your faith is worthless; you are still in your sins.” (1 Corinthians 15:16–17, NASB95)

The word “worthless” here means “vain, empty, fruitless, aimless. It is building houses on sand, chasing the wind, shooting at stars, pursuing one’s own shadow” [Complete Word Study Bible].  In short, it is not what we who follow Christ are aiming at, we are aiming at vibrant, genuine faith, not empty and worthless.

Here’s the thing, everything rests on Christ.  We cannot conjure faith out of the air or making something vain and fruitless into something worthwhile and fruitful, that is not the nature of faith.  Faith is granted; it is a gift:

For by grace you have been saved through faith. And this is not your own doing; it is the gift of God,” (Ephesians 2:8, ESV)

Worthless faith is faith that rests on anything but Jesus Christ and him crucified; true faith is a gift, granted by a gift-giving God and sits on the firm foundation of the work of Christ on our behalf, on his death for our sins, on his resurrection to new life.