Since Gnostic is a term that has been applied in a number of ways, I can't be certain what the church you are thinking of joining believes. However, historical Gnosticism is largely a repackaging of Neoplatonic nonsense that treats the physical world as bad and an idealized abstract spiritual world as good.
Neither Neoplatonists nor gnostics regarded the spiritual world as abstract; they regarded it as something which, with the right practice, a person could experience directly. In fact, if there's one thing Neoplatonists, gnostics, and Nicene Christians could all agree on, it's that the spiritual world is far more real than the material world.