Assuming the accuracy of the quote, and without knowing the context of this remark from Abu, several things come to mind. Before listing them, I'm assuming that the prima facie meaning of "the book" as a reference to the Qur'an is correct, making "the sword" either that of Mohammed or of Muslims in general.
1) Muslims believe that the Qur'an is a miraculous work of Allah, the greatest proof of the truth of Islam, and, therefore, the greatest single factor or motive force in swaying people to become Muslims. However, the Qur'an has in fact never been an especially effective tool in seeing people, societies, and nations turn to Islam; the distinguished tool that gets this prize is the sword, first wielded by Mohammed (and his companions), and then later by his dutiful followers. It is an undeniable even if uncomfortable fact that the nations' people that converted to Islam did not do so through the means of peaceful Qur'anic suasion. Instead any and every nation, with few possible exceptions, that has ever embraced Islam, beginning with what was then (and still is) pagan Arabia (for it just swapped one form of paganism for a suped up Mohammedan version) down to the present day, has always and only converted by force and through much bloodshed and cruelty.
2) Since the Qur'anic text itself was determined by the sword under Uthman, the book only says what the sword of a certain faction determined for it to say.
3) If a Muslim wants to be sure of entrance into paradise, the only means this side of that great harem in the sky is through Jihad in the cause of Allah, i.e., through the act of fighting and spilling the blood of infidels rather than through faith or trust in the person and deeds of Allah or even by means of conformity to Allah's character and/or will as revealed in the Qur'an.
Hence, if you want to know about the veracity and real character of Mohammedanism, then you must ultimately look past all the idle remarks and spilled ink about mercy and compassion and look to all the spilled blood instead, especially when the ink is not without copious references to the sword anyway.