Read It & Believe It
Do you believe that there is a G-d? Do you believe that He created the world? Do you believe that He gave the Torah to the Jewish People? Do you believe that it was Moshe Rabeinu who received the Torah and transmitted it to us? Do you believe that the prophecy of Moshe Rabeinu is true? Do you believe that Moshe is the chief among prophets, both those who preceded him and those that followed him? Do you believe that the Torah in our hands is the authentic Torah?

Good start. If you answered NO to any of the above, then the point of this Lead Tidbit might be lost on you. But if each question got a YES, then let's proceed to the next stage.

If someone were to say to you that there is no G-d, you would stand strongly and tell him that he is wrong or mistaken. If someone denies that G-d created the world, you should be sure enough of your beliefs to quote B'reishit Bara Elokim... and continue from there. The fact that there are other people who do not believe that the world was created by a Supreme Being should not weaken your belief in G-d's creation one bit. If it does, then you have the challenge of the mitzva of Belief in HaShem to work on your doubts.

If a fellow Jew expresses to you his doubts about Shabbat, for example, you should be able to work with him, armed with the relevant p'sukim from the Torah and then the Mishna, Gemara, Shulchan Aruch, etc.

So when the nations of the world, or some of our fellow Jews, question our exclusive claims to this Land, how about reading this week's sedra (and many more portions of the Torah) about G-d speaking to Bnei Yisrael through Moshe Rabeinu, and telling us that we will be crossing the Jordan into the Land. That we shall vanquish the inhabitants of the Land and destroy their idolatry. That we shall acquire the Land and dwell in it, because G-d has given it to us. And then stand proudly and say without hesitation – just as you would (should) say about G-d's creation and about the Shabbat – that this Land is ours. It belongs to the Jewish People and only to the Jewish People. That the claims of others are invalid. 

And then turn the page and read G-d's words about the boundaries and believe with all your heart that these words are as true as any others in the Torah. People will argue these points, and even fight us on them, but the Torah is truth and worthy of our belief and defense.