Hi Vincenzo,
Try :
\version "2.18.2"
\header {
title = "song title"
}
\score {
\new Staff \relative c' { c4 }
}
% I WOULD LIKE TO HAVE MORE VERTICAL SPACING HERE
\markup {
%% put some space here:
\vspace #20
\fill-line {
\hspace #1
\column {
\line { O sacrum convivium }
\line { in quo Christus sumitur, }
% I WOULD LIKE TO HAVE AN EMPTY LINE OR MORE HERE
\line { futurae gloriae nobis pignus datur. }
}
\hspace #2
\column \italic {
\line { O sacred feast }
\line { in which Christ is received, }
}
\hspace #1
}
}