Abdullah ibn Ibraaheem ibn Saif who showed him(Ibn Abdul-Wahhaab) his books and described them as the weapon that he had prepared for the people of Majmah. In fact, in one letter, he advised, Perhaps the enemies of tauheed have much knowledge, many books and proofs, as Allah says,
“Then when their Messengers came to them with clear proofs, they were glad (and proud) with that which they had of the knowledge (of worldly things)” (Ghaafir 83).
If you recognize that fact and if you recognize that the path to Allah must have enemies sitting upon it who are people of eloquence, knowledge and argumentation, as Allah says,
“And sit not on every road, threatening, and hindering from the Path of Allah” (al-Araaf 86),
Then it is obligatory upon you to learn of the religion of Allah what will become weapons for you by which you may fight those devils.
At the same time, though, he also understood that if one relies upon the revelation from Allah, one cannot truly be defeated by any kind of argument. Hence, one simply has to study the truth and then present it without any fear. Thus he wrote, “But if you turn to Allah and submit to the arguments of Allah and their exposition, then you should not fear or grieve. Verily, the plot of Satan is weak. A commoner from the true monotheists can overcome one thousand of the scholars of those polytheists, as Allah has said,
‘Verily, our troops are those who will overcome’ (al-Saaffaat 173).
The soldiers of Allah overcome others through proofs and speech in the same way that they overcome them with swords…”
Reference: Muhammad ibn Abdul-Wahhaab, Muallifaat, vol. 7, p. 156, 240, 280-284