It is noteworthy that God is referred to six times in this sidrah as Tzur, "a rock". Even though other books of the Bible and various liturgical texts describe Him in this way, this is the only place in the Torah where this terminology is employed.
There are several reasons why God might be described as a rock. Firstly, a rock is something which is strong and powerful. It can't be easily damaged and it leaves its imprint on whatever it comes into contact with. Likewise, God's omnipotence cannot be easily harmed by human waywardness and His power is evident in so many aspects of the world. Secondly, rocks have been on the face of the earth since time immemorial and they don't fade or die. So describing God as a rock is a way of referencing His immortality and illustrating that He has always been present and that He will endure forever.
Some commentators suggest that in this context "rock" is an inaccurate translation of the word tzur. Rabbi Yaakov Mecklenberg (1785-1865) asserted that it should be regarded as a reference to God as the creator of the world, yotzer. He further suggested that tzur is related to the word litzror, which means to tie something together. God is called Tzur Yisrael because the destiny of the Jewish people is tied to Him.
This year, because Ha'azinu is read after Yom Kippur, the haftarah is the Song of David (II Samuel 22). It is usually assumed that the parallel between the haftarah and sidrah is that both passages are called songs. But it is also possible that the Song of David was selected because the word tzur appears four times in the passage as a reference to God.