Rise up—for you the flag is flung—for you the bugle trills;
For you bouquets and ribbon'd wreaths—for you the shores a-crowding;
For you they call, the swaying mass, their eager faces turning;
Here Captain! dear father!
 This arm beneath your head;
It is some dream that on the deck
You've fallen cold and dead.
3
My Captain does not answer, his lips are pale and still;
My father does not feel my arm, he has no pulse nor will;
The ship is anchor'd safe and sound, its voyage closed and done;
From fearful trip, the victor ship, comes in with object won;
Exult, O shores, and ring, O bells!
 But I, with mournful tread,
Walk the deck my Captain lies,
Fallen cold and dead.
Ties together the images of  “exulting” crowds  from stanza 1 and  ringing bells  from stanza 2. 
 Whitman suggests that celebration of the Union victory should continue despite grief over Lincoln’s death. In the final lines he seems to take the burden of mourning onto his own shoulders, as a kind of poet-spokesman for his nation.
O Captain My Captain