This is a poem about whether there is eternal life (life after death). In the first two lines, speaker reflects on the fact that when her loved ones die the news of a death is delivered so fast and widely and sadly can't be ignored.
Likewise, if someone were to rise from the dead (If those I loved were found"), church bells would toll to tell the news of miracle.
But if these sleepers lie buried, blooming
daisies at the graveside would speak for them.
After her Philip parted unwilling with life, his parting drilled into her heart without the need
for daisies.