Teaching the cause of God is Baha'i language. I was never a particular good Christian, and I'm a marginally better Baha'i. Regardless, sometimes I acted in accordance with what I sincerely believed God wanted me to do. On one occasion that involved standing in a crowded University area and providing a testimony as to why I had become a Christian. I do recall not long after a woman approached me on the street. Evidently I had talked to her about Christ and she had decided to give her life to Jesus. I had absolutely no recollection as to what I had said. I believe sometimes God makes use of us despite all our failings and imperfections to assist another soul gain a glimpse of the Almighty or 'Teach the Cause of God'.
As a Christian I never properly studied the book of Joshua. As a child attending bible classes one of the songs we sang were about the walls of Jericho coming tumbling down. I never made the connection it being about a genocide God had commanded the Hebrew people to carry out. As I understand it the Mosaic Teachings were in part preparatory for the Hebrew people to invade and possess the land of Canaan, and to make it their home. Another aspect was laws that would enable them to live in the land in accordance with what God commanded. Both aims were achieved, culminating in the Davidic kingship. This in turned prepared people to accept the Teachings of Christ when He came. The same can be said of Muhammad and Baha'u'llah.
It was harsh times 3,500 years ago and the moral standard was very different to what it is now. On reflection the military approach used, as bloody as it was, sent a clear message to the peoples who inhabited the land who was in charge, and the consequences of trying to retake their land. Its problematic when we judge people of the past by our moral standards. We often take this approach with Islam too.
Hope that helps and sorry to ramble on.