What is poet saying in this stanza of Piano?So now it is vain for the singer to burst into clamour With the great black piano appassionato. The...

The speaker is saying that it is in vain for the singer to
try and entertain enthusiastically. The singing and music has taken the adult man down
childhood memory lane. The speaker is reminiscing about childhood days and cannot help
but weep.

The speaker cannot join the singer's clamorous
enthusiasm. The speaker is in another time frame. He has revisited childhood when his
mother played the piano and sang on a cold Sunday evening. The adult speaker is right
back underneath the piano stool, near his mother's feet. He is remembering a precious
time in his life as a child. It brings back such fond memories until he can only
weep.

The speaker has traveled back down the road to his
childhood. He has put aside his manhood and broken down, weeping for days gone by. The
speaker's heart is wrenched at the moment. He can only long for the days when his
mother's tender voice had a soothing effect on him. It is in vain for the present day
singer to try and  rally enthusiasm from her audience. It is in vain for the present day
singer to try and entertain in a delightful manner. The speaker is already back in his
childhood, sitting underneath the piano, at his mother's feet. The adult man wipes away
his tears:

So
now it is vain for the singer to burst into clamour 
With the great black
piano appassionato. The glamour 
Of childish days is upon me, my manhood is
cast 
Down in the flood of remembrance, I weep like a child for the
past.