וְעָשִׂ֥יתָ בְרִיחִ֖ם עֲצֵ֣י שִׁטִּ֑ים חֲמִשָּׁ֕ה לְקַרְשֵׁ֥י צֶֽלַע־הַמִּשְׁכָּ֖ן הָאֶחָֽד׃
Farás travessas de madeira de acácia: cinco para as tábuas de um lado do Mishcan,
Siftei Chakhamim
The distance from the border, etc. You might ask that based to this division, the land would be divided into four sections! The answer is that the distance from the border until the second town of refuge is the same distance as from the first town until the last [town]. And from the second town until the second border is also the same as these distances. Therefore it is called “three sections.” I gave the same explanation in parshas Terumah (Shmos 26:26) regarding the bars. It also explains in Perek Eilu Hein Hagolin (Makkos 9b) [like Rashi here], that “divide into three sections” means that the land is divided into four sections along its breadth. See there.