Snow White Part1

A very long time ago, in mid winter, when the snowflakes were falling like feathers from heaven, a beautiful queen sat sewing at her window, which had a frame of black ebony. As she worked, she looked sometimes at the falling snow, and it happened that she pricked her finger with her needle, so that three drops of blood fell upon the snow. How pretty the red blood looked upon the dazzling white! The Queen said to herself as she looked it, “Ah me! If only I had a dear little child who had skin as white as the snow, lips as rosy as the blood, and hair as black as the ebony window-frame.”
Soon afterwards she had a little daughter, with skin white as snow, lips rosy as blood, and hair as black as ebony– and she was therefore called “Little Snow-White.”
But alas! When the little one was born, the good queen died.
A year passed away, and the King took another wife. She was a beautiful woman, but proud and haughty, and she could not bear that anyone else should surpass her in beauty. She had a mirror and when she stood in front of it and asked,
"Mirror, mirror upon the wall, Who is the fairest of us all?"
the mirror answered-
"Thou, Queen, art the fairest of all,"
and the Queen was contented, because she knew the mirror could speak nothing but the truth.


Words

1.mid/中間の、中央の
2.snowflakes/雪片
3.sewing/縫う、裁縫
4.ebony/漆黒の、真っ黒の
5.pricked/(prick)刺し傷、突き傷、ちくちく痛む
6.needle/～をからかう、ちくちくといじめる
7.drops/点滴薬
8.upon/onと同じ
9.dazzling/目も眩むばかりの、まぶしい、眩惑的な
10.dear/敬愛する、いとしい、かわいい
11.rosy/バラのような、薔薇色の、有望な
12.afterwards/後で
13.therefore/従って、それ故に、その結果
14.alas/まあ！
15.haughty/おうへいな、傲慢な、偉そうな
16.bear/運ぶ、耐える、我慢する
17.surpass/優る、凌ぐ、超える
18.fairest/最も公平な
19.contented/満足した、満足している

Question
I can't understand [the mirror could speak nothing but the truth.]'s meaning.


Snow Whitehttp://storynory.com/2006/07/31/snow-white/