The late invasion of Virginia by Capt. John Brown and his company has, with all its concomitant circumstances, excited more attention and aroused a more thorough spirit of inquiry on the subject of slavery, than was ever before known. As this is pre-eminently a moral question, and as there is no neutral ground in morals, all intelligent men must ultimately take sides. Every such man must either cherish and defend slavery, or oppose and condemn it, and his vote, if he is an honest man, must accord with his belief. On a question of so momentous importance, "Silence is crime." It demands and will have a thorough investigation, and all attempts to stifle discussion will only accelerate the triumph of the cause they were designed to crush. Thus the denunciation in Congress of Mr. Helper's book, which is in substance only an abstract of facts taken from the last census of the United States, has operated as an extensive advertisement, and will be the means of circulating thousands of copies, where, without such denunciation, it would never have been known. There is in the North, as well as the South, a class of men who act, apparently, on the supposition that those who foresee and foretell any calamity are as guilty as those who create it, and that the only way to obviate any impending danger is not to see it. Such persons not only refuse to see and hear themselves, but do what they can to keep their neighbors in like ignorance. It has been truly said that "the power of slavery lies in the ignorance, the degradation, the servility of the slaves, and of the non-slaveholding whites of the South, and of the corresponding classes in the Free States. It is through this ignorance and servility that the slaveholders manage to dictate to ecclesiastical bodies, to have power to control pulpits, presses, Colleges, Theological Seminaries, and Missionary and Tract Societies." To keep the blacks and non-slaveholding whites in ignorance is, doubtless, the reason why such pains are taken in Congress to prevent the circulation of Helper's book at the South, which was compiled by a non-slaveholder for the special benefit of the men of his class. The population of the Free States is now about eighteen millions; of the Slave States, eight millions. The slaves number about four millions, who are held as property by only 347,545 persons, men, women and children. This number, small as it is, constituting about one sixth part of the United States, have thus far controlled the legislation of the country. How this power has been acquired is easily understood when we examine the false ideas respecting slavery which are everywhere prevalent; such as the weakness of the public conscience, in the absence of a practical and experimental knowledge of the truth of God's word--in the atheistic notion, prevailing even in the Church and in the ministry, that the unrighteous enactments of wicked me are paramount in authority to the commandments of the Great Jehovah.