The meaning of the 23rd line “"Mother whose heart hung humble as a button" in the poem “War is Kind” by Stephen Crane is that this mother humbly accepts what war does to families. The meaning here in this line is that this mother, while not totally believing in war, does accept that men and women do go to war and that loss ensues and must be accepted. There is really nothing she, nor other mothers can do about this.
This 23rd line has to be looked at in the context of the rest of this poem. Only then can the power and meaning of this line really come through. The poem talks of great battles and heroic acts that take place in war, where soldiers sacrifice for others and confront their enemies and their own fears, such as is conveyed in the line:
“These men were born to drill and die.”
However, the people left behind, while others go off to war, realize that war also consists of “A field where a thousand corpses lie.” There is no beauty or glory in war. Mothers on both sides of a battle lose their sons and/or daughters in war. It’s as if the mothers are to accept this patiently, enduringly, and humbly. This is why Stephen Crane says that the mother has a humble heart as she looks at the “…bright splendid shroud…” of her dead soldier son.
The poem has a somewhat sarcastic tone to it when it says that one should point out to the soldiers the “virtue of slaughter.” There is no virtue whatsoever in slaughter – it is a reviling, destructive, and sickening thing. In addition, there is nothing positive about killing and about Man always being in contention with Man.
But, again, this poem, in the 23rd line, is saying that mothers almost have to look the other way - away from the horrors of war - and humbly accept that their husbands and sons and daughters do go off to war at the behest of the nation’s government and there is valor in accepting the call to defend one’s country and fight for freedom.
This is where the patient acceptance and humbleness of the mother comes in - a mother who must look down upon her dead son and deferentially know and hope that the ultimate cause was at least somewhat worthwhile. Nonetheless, a mother, or anyone else who looks at war critically, will never really totally accept that war is the answer to disputes, as war breeds more war and is the never-ending saga of humankind from its beginnings to this very day.