Celie never learns, or at least she doesn't tell God, what finally persuades Sofia to marry Harpo and make a home for him and their baby boy. But once they are settled, Celie studies this strange black woman who is unlike any woman whom Celie has ever known. Celie's word for Sofia is "solid." It is a quality that Celie is clearly unfamiliar with, because, at one point, childllike Celie tells Harpo to beat Sofia. Seemingly, Celie wants to see if Sofia will break.
Sofia, of course, doesn't break — but Celie has never been broken either — except in Celie's case, everyone assumes that her will has already been broken, if indeed it ever existed. Celie may act submissively, however, but she has always reacted to beatings, without knowing it, in much the same way that Sofia does. Objectively, one can see that Sofia is "solid." No one suspects, however, that when Celie is beaten, she too is "solid"; she imagines that she is wood and absorbs the violence inflicted on her — but she doesn't break or become bitter. In her own words, she says stoically, "I don't fight . . . but I'm alive."
When Harpo attempts to break Sofia's will, he is clearly the bruised loser, and note here how humorously, and yet how all too accurately, he explains that he had a run-in with a mule. Consider Sofia and the theoretical mule. Sofia and a mule are not too different. Both must do fieldwork and both are stubborn. Also, a mule is as much a female as it is a male. And Sofia is as much a woman as she is a man. She is both a mother and a fighter.
Year after year, Harpo continues to try and tame Sofia, and yearly, he loses — bruised but stubbornly determined to make his woman a slave to him. Finally, Celie witnesses Harpo's bruises one time too many, and deep guilt festers within her Christian soul; she knows that it was she, along with Mr. ________,who urged Harpo to beat Sofia in the first place.
Letter 21, then, is a key letter; it contains one of the most significant scenes in the novel: Sofia confronts Celie. Sofia has learned that Celie told Harpo to beat her, and she reveals how terribly betrayed she feels. It is one thing to have a man try to beat you; it is quite another thing to have a woman betray another woman. Sofia trusted Celie because Celie seemed like a kind woman. Sofia believed that there was a special bond between them, as women, and now she has learned that a woman urged a man to do her harm. A woman should know better; as Sofia says, "A girl child ain't safe in a family of men."
This raw exchange between the two women is significant because of their well-defined, vividly contrasting characters. Sofia is a fighter — loudly independent and sharply decisive. Celie is a timid shadow — quietly anguished as she admits to having been a fool. Sofia cannot understand Celie's motivation; both women were reared in similar domestic situations, but Sofia has always been filled with angry aggressiveness, diametrically unlike the passive, mother-like, spiritual Celie. Sofia's advice to Celie is loud and clear: "You ought to bash Mr. ________ head open. Think about heaven later."
Laughing together, the two women are reconciled finally because there has been an honest exchange of viewpoints between them, and their reconciliation is symbolized by the quilt that they decide to make together. A quilt, after all, is a collection of many colors and fabrics sewn by a single thread, and the new union between Celie and Sofia will be sewn with a new, strong thread of love and trust.