Superstition is the notion that supernatural powers created our world and interfere with its operations. 
Fear of such gods and their will is banished with understanding.
By showing that the operations of the world can be accounted for entirely in terms of the regular, but purposeless motions of tiny atoms and agglomerations of atoms in interaction in empty space.
The fear of death will be banished by showing that death is the dissipation of a being's material mind.
And so, as a simple ceasing-to-be, death can be neither good nor bad for this being.
The value of life for a being is something that only matters to this being during its life.
Fear of death is a projection of terrors experienced in life, of pain that only a living (intact) mind can feel.
Lucretius also puts forward the 'symmetry argument' against the fear of death.
In it, he says that people who fear the prospect of eternal non-existence after death should think back to the eternity of non-existence before their birth, which they probably do not fear.