Witnessing. ( Isaiah 55 v 10 -11 )

Often I have witnessed to those in the cults,J Ws, Mormons,it is very challenging ,often I became  frustrated with them,as they twisted the truth , and so often they were obviously not listening to what I had to say.On reflection it all seems to have been a waste of time, who knows ,my witness may bear in a coming day. I have also witnessed to many people again very little response, again I ask myself was it a waste of time?.  Yes it may have appeared to have been a waste of time,but I will still witness to people,I am not a prophet ,but as I read about those who were prophets ,they had a thankless task. Take one of the greatest of the prophets,Isaiah ,we read of his call to his ministry in Isa 6 , where he responded to God asking the question.'Whom shall I stand?,'And who will go for us?' Isaiah replied ,''Here am I ,Send me!'. God answers, 'Go and tell this people'. And what follows appears that they would not respond, and in fact they were going to be judged,so it was to be a very challenging task that Isaiah was called to take on.Tradition has it he was put to death probably under wicked King Manasseh's rule.Jesus said we are to be his witness'es Acts 1 v 8,so we must be faithful to that,yes all God requires of us is faithfulness,even if people don't respond, even if we have to suffer,yes even death.