Of course, our literature is important and should be offered in the field. The Bible, however, is our primary tool.
وَمِنْ ثُمَّ كُنْ مُسْتَعِدًّا لِقِرَاءَتِهَا وَأَنْتَ تَكْرِزُ مِنْ بَابٍ إِلَى بَابٍ .‏