Isn't this Ritsos' vision of the risen (ορθοί ξανά) dead who join the fight? Full of strength, they tread contemptuously on death, as if their deaths were in their way to, or paved their way to, the front lines. The ecclesiastical echo may be intentional, though slightly ironic.
The line reminds us of Ritsos' attitude toward heroic death, which is not death but resurrection, as in e.g. Romiosini Canto I:
all killed and no one dead,
their eyes are shining in the upper fastnesses.
and Canto IV:
Under the earth, between their crossed hands,
they hold the bell-rope. They await the hour, they're not asleep,
they're waiting to announce the resurrection. That soil
is theirs and ours: no one can take it from us.