The fourth aliyah discusses some aspects of cleanliness of the Jewish camp, because, as the Torah says here, G-d walks in the Jewish camp.
Included here is the Torah prohibition of female prostitution and male sodomy. It also prohibits here the loaning for interest to a Jew, but interest may be charged to a non-Jew.
Finally, this aliyah says that everything that comes out of one's mouth is like a vow, and must be carried out. Therefore, we must always be careful to say "blee neder" (without a vow), or "Im Yirtze Hashem" (G-d willing) whenever we say we're going to do something. This is so that if it turns out we are prevented from doing that thing that we said we would do, we won't be breaking a vow. In a similar vein, Judaism says that we can never underestimate the power of a blessing, or (G-d forbid) of a curse, of even a simple Jew. The power of our blessings should not be taken lightly, and we are forbidden from ever uttering a curse.