How did he establish the borders of the land?
Rashi: He established their land with every good thing.
Radak: This refers to the seven landscapes of the world. Each has a different climate; all is needed for the creations.
Why does it mention summer and winter?
Rashi: This is like "Shavu'os Chukos Katzir Yishmor Lanu" (Yirmeyah 5:24). You did not change for us the order of years.
Radak: Also this is a matter and its opposite. It did not mention cold and hot, for this is included in summer and winter. Day and night are due to the constant (daily) orbit of the sun; summer and winter are due to its periodic (annual) orbit.
Malbim: Also the annual motion of the sun, from north to south and from south to north along the line of the Mazalos, is from You. Via making the sun veer [from the equator], this causes summer and winter, and enables settling the lands in the north and south 1 .
Perhaps he means that if the sun was always over the equator, the entire year lands in the north and south would not get enough sunlight to make crops grow. (PF)
