Hi Ryan,
Woobadooba has given you some good advice. Let me explain.
The very first thing that any Christian must understand about theology, religion, and doctrine, is that none of these can be "proven." That includes the writings of Ellen White.
Theology is not like mathematics where if you follow the steps of correct calcuclation there is only one answer that is correct for each problem. This is not to say that there is no correct answer for biblical questions. What it does mean is that just like the plan of salvation, each and every one of us must be willing to accept those biblical teachings that are correct and will help us understand God's will and what is needed for salvation. If it were possible to prove these things there would be no need for faith in the sacrifice of Jesus Christ. People would be "forced" to believe in the the existence of God, and the need for Christ death on the cross. To be "forced" to belie these things would mean that man doesn't truly have free will which would nullify the entire plan of salvation.
For these reasons you should first introduce others, that do not yet know him, to Jesus Christ as a personal friend and Savior. As you yourself learn to grasp the great theological concepts that Christ himself taught, your own faith and understanding will be greatly increased.
Once you can defend, and explain, your Christian beliefs from the Bible only, others will see the love of Jesus Christ in you and will be far more receptive to listen to what else you have to say.
There is a saying that I use all the time; "A man convinced against his will is of the same opinion still." It is impossible force another person to believe something that they don't want to believe. Again, the evidence of God's gift of free will.
May God put His loving arms around you, the Holy Angels protect you, and the Holy Sirit guide as you study God's word.
Your friend and brother in Christ,
Doc
Doc,
I didn't mean to imply that one can't prove something to be true; rather, there are certain people that have such a bad attitude about certain topics that it won't matter what you say to them, they will still try to shoot you down, because they have already determined that they can't be wrong.
I don't think it is so much an issue of you can't prove 'anything', as it is an issue of what basis it is that people are willing to accept as a means to disclose proofs for a belief in something.
For example, if someone accepts the Bible as inspired by God, then one could teach that person the proper methods for interpreting scripture, and thus demonstrate how an interpretation of a passage can test a certain doctrine, or idea, and thus determine if it is true or false.
If this weren't true, then Paul's words in 2Tim. 3:16 would have been pointless, since scripture can be used to correct and rebuke those who are in error.
On the matter of Ellen White, it's not that you can't prove she was a prophet; rather, it's a matter of what basis people are willing to accept as a means to make that determination.
It's the same when dealing with an atheist. If that person is willing to accept a solid basis of reason as a means to make the determination that God exists, then one could use reason to prove that God exists (just read C.S. Lewis's 'Mere Christianity' and you will see what I mean). It's just a matter of what that person is willing to accept. And this is where the issue of intellectual honesty comes into play.
For example, I can prove without a shadow of a doubt that the phrase, "You can't know the truth", is false, simply by using reason. If one says you can't know the truth, how is it then that he even knows that what he's saying is true?
He obviously believes that it is true to know that you can't know the truth. So he thereby defeats his own claim by contradicting his own belief with his own belief.
Now if he is willing to accept the fact that one could use reason as a means to prove that what he had just said is false, he would necessarily have to agree that he just proved that one can know the truth. However, whether he accepts it or not, he just proved something--that he didn't think is argument through properly.
So it's not so much an issue that one can't prove something about something else, as it is an issue of what basis people are willing to accept as a means to prove anything at all.
In short, we can prove things to be true, even the existence of God; but we can't make people agree that such means that we are using to prove these things are absolute.
What it all comes down to really, is intellectual honesty. Some people are honest, and others are not. Of course, it could also be an issue of what people are capable of comprehending. But whether they are honest, or not, or are capable of comprehending reasonable arguments, or not, makes no difference, because the truth is the truth. In other words, 2+2 will always = 4. Just because someone who is unlearned in math can't fathom this, that doesn't mean it is false, or unprovable. It just simply means that he needs to learn something about something that is true, in order to see it for what it really is--the truth.
So it's not an issue of can one prove what is true; rather it is an issue of who you are trying to prove it to.