Why are two different expressions of speaking used for the heavens and the earth?
(32,1) “Listen, O Heavens, and I will speak; and hear, O Earth, the words of my mouth.”
The reason why it uses an expression of דבור with regard to the heavens and an expression of אמירה with regard to the earth, is because the heavens connote masculinity, penetrating the earth and causing it to give birth (to produce), and the earth becomes pregnant and gives birth (produces) like a female, as it teaches in the gemora Ta’anis 6b.
And דבור is a harsh expression and אמירה is a gentle expression, as Rashi explains in several places, for example in Bamidbar 12:1.
And we see at the giving of the Torah that a harsh expression was used for the males and a gentle expression was used for the females, as it says in Shemos 19:3 “Thus you shall say (תאמר) to the house of Ya’akov (these are the women - say it to them in a gentle manner) and speak (תגיד) to the sons of Yisrael (the punishments and the fine details of the laws explain to the males, matters that are tough as sinews - גידין)”, as Rashi explains there.
Hence, the two different expressions of speaking that are used in our posuk are completely appropriate.
Who is allowed to explicitly say the four letter name of Hashem?
(32,3) “When I call out the name of Hashem, proclaim the greatness of our G-d.”
Rashi explains that from here the Rabbis in the gemora Ta’anis 16b learned that after every blessing that is recited in the Beis Hamikdash (“when I call out the name of Hashem”) the people should respond “Blessed be the name of His glorious kingdom forever and ever” (“proclaim the greatness of our G-d”).
The reason why this teaching is restricted to the Beis Hamikdash is because “the name of Hashem” here refers to the four letter name of Hashem which is only permitted to be explicitly pronounced in the Beis Hamikdash by the Kohen Gadol.
But it is possible that Moshe Rabbeinu also mentioned it everywhere, and therefore it says “When I call out the name of Hashem”, according to Rashi’s explanation of the first word of the posuk.