Fourth aliyah consists of the last two aliyot of parsha Behar and the first two aliyot of parsha B'Chukosi. Here we are given the law of the Jewish bondsman who, because of his poverty, sells himself to us. In short, we are not permitted to treat them with rigor as with slaves, but on the contrary, we are to treat them as hired servants doing reasonable and necessary work, and they are to be released in the Jubilee year.
The aliyah continues with the laws of a non-Jew who becomes rich. Rashi interprets this, as the non-Jew became rich by clinging to you. Similarly, we have here the law of a Jew becoming poor, which Rashi interprets: the Jew became poor by clinging to the non-Jew and learning from his doings. The aliyah continues: the Jew sells himself to the non-Jew, the Jew may be redeemed by his relatives and the Jubilee year releases him.
The aliyah then mentions the prohibition of not making an idol. Rashi says this is mentioned here, in proximity to what we just read about, where a Jew who is a bondsman of a non-Jew, so that the Jew shouldn't forget who he is and despite who his master is, he still must keep the Sabbath, not worship idols, etc.
The fourth aliyah continues into parsha B'Chukosi. Rashi says the words "Im B'Chukosi" refers to the study of Torah. This aliyah promises blessings for studying Torah for the purpose of doing the commandments, and then doing them (the commandments). The blessings include plenty of food, and rain at the proper time, peace from enemies, and from beasts. Here the Torah says five of us will chase one hundred enemies; one hundred of us will chase ten thousand enemies.
