The colours of the Battle Flag are in fact those of the British Union Flag, but interpreted as emblems of American republicanism. Miles, on presenting the Stars and Bars to Provisional Congress:
The cross is both the constellation Southern Cross, pointing away from the North, and the symbol of a revealed religion endorsing slavery. It was turned diagonally to make it more acceptable to protestants and Jews. In its new form, Miles even discovered some additional value:The three colors of which its is composed, red, white and blue, are the true republican colors. In heraldry, they are emblematic of the three great virtues.—of valor, purity, and truth. (Preble p.506)
the 'saltire' of heraldry, significant of strength and progress (from the Latin salto, to leap). (Preble p.514)The stars represent the States in the Confederacy, forming (yet another) "new constellation in the firmament of nations".
On November 6, 1865, at Liverpool, England, CSS Shenandoah lowered the last Confederate Flag, the naval version of the Stainless Banner that had succeded to the Stars and Bars.
Our idea is simply to combine the present battle-flag with a pure white standard sheet. (...) As a people, we are fighting to maintain the Heaven-ordained supremacy of the white man over the inferior or colored race; a white flag would thus be emblematical of our cause. Upon a red field would stand forth our Southern Cross, gemmed with the stars of our confederation, all combined, preserving in beautiful contrast the red, white, and blue. (Preble p.524)and five days later
Such a flag would be a suitable emblem of our young confederacy, and, sustained by the brave hearts and strong arms of the South, it would soon take rank among the proudest ensigns of the nations, and be hailed by the civilized world as THE WHITE MAN'S FLAG. (Preble p.525)
The Confederate States of America died a violent death at the hands of invading armies in 1865, and thus it was "proven" that secession was wrong... that no portion of the American people could elect a path of political self-determination so long as a more powerful section opposed them. (...)
The flags of the Confederacy represented the aspirations of a brave and resourceful people who determined to strike out on their own and carve their place among the nations of the earth. Their desire to live under a government based upon "the consent of the governed" should be respected; and their tenacity in attempting to preserve their chosen government, though in vain, must be admired. The people of the Confederate States of America earned for their flags an honored place among the sacred relics of human endeavor. (Cannon, p. 73)