Because I said so... saith the Lord

Maybe it was just me, but I remember when I was a kid, I never wanted to make my bed. Sure, I'd clean my room but making the bed seemed pointless. I mean, sure it looked nice when your room was clean but what happens at night? you mess it right back up again! and you'd have to do it all over again so what was the point? I always got the profound words from my mother "because I said so..."
For my Christian Doctrine class, I had to read Evangelism and the Sovereignty of God and had to write a paper from what I concluded from the book. which tried to answer the question of if God is Sovereign, why do we as humans need to "go ye therefore..." I believe every Christian has succumbed at one time or another to the mistaken belief that we are somehow responsible for the results of our evangelistic efforts. When we speak with a friend for hours and share our faith with that person but are able to secure no prayer of faith and repentance, we assume that we have done something wrong. We assume, perhaps, that our arguments are not persuasive enough or that we do not believe strongly enough what we claim to believe. But, thankfully, this is not the case. We are responsible to present the gospel faithfully and forcibly, but are not responsible for the result. When we have finished our task, we are to rejoice regardless of any result - we should rejoice as much if we have seen no conversion than if we have. In either case we should rejoice in the opportunity God gave us to share the awesome truths of His Word and to be faithful servants. We can rest in the confidence that we were faithful and can know that His will will be done.
I'm not saying that we all have to do it the same way...but we do. The question is still Why do we have to give a “clear and forciable” presentation of the gospel when we acknowledge that the clarity and foribleness of the presentation have nothing to do with the end result? All I can think of is "Because God said so..."
Ok, I think I'm done pretending I'm smart now...