What is the meaning of "Al Tevahel Al Picha"?
Ibn Ezra: In front of Him, in His house, do not say words b'Vahalah 1 (quickly - Ibn Ezra 7:9, Metzudas Tziyon).
Rashbam: When you pray, do not say too many words.
Rid: Even if you did not sin, and you want to vow Korbanos, be careful how you vow, lest you vow something that you cannot fulfill, and you will transgress your vow.
Seforno: Do not pray via habit of the tongue.
Metzudas David: Do not rush to say complaints against Hashem's Midos.
Metzudas Tziyon: "Al Picha" is like Al b'Ficha, just like "v'Sugeru Al Masger" (Yeshayah 24:22, is like b'Masger).
What is "rushing the heart"?
Ibn Ezra: Saying something before understanding it. The heart is like lost and straying in worldly affairs. Therefore, Mashi'ach Hashem (David) said "Matza Avdecha Es Libo" (Shmuel II, 7:27).
Seforno: It is to say words of Tefilah before your heart intends for it. Early Chasidim would delay an hour before praying, in order to have intent in their hearts (Brachos 30b).
Metzudas David: Even your heart should not rush to entice you to complain against Hashem's Midos.
What is "Lehotzi Davar Lifnei ha'Elokim"?
Rashi: To speak harshly in front of Him. Ri Kara - Dor ha'Midbar said "Oh ba'Midbar ha'Zeh Lu Masnu" (Bamidbar 14:2), and they were answered "Im Lo Ka'asher Dibartem b'Aznai Ken E'eseh Lachem; ba'Midbar ha'Zeh Yipelu Figreichem" (ibid. 28-29).
What is the significance of "Ki ha'Elokim ba'Shamayim v'Atah Al ha'Aretz"?
Rashi citing Koheles Rabah: Even if a weak person is above and a Gibor below, the Gibor fears the weak 1 , and all the more so [here], the Gibor is above and the weak is below!
Ibn Ezra: He stands over you, sees you and hears your words. He is in the highest place, and you are in the lowest.
Rid: He is strong to exact payment from you [if you transgress your vow].
Seforno: Hashem dwells in all of Shamayim, for he is not physical. You are in a particular place, like is proper for physical matters. You cannot quickly (easily) direct your Da'as to Him!
I.e. the one below fears the one above. (PF)
What do we learn from "Yiheyu Devarecha Me'atim"?
Brachos 61a: A person should say few words in front of Hashem (Maharsha - he should not pray excessively for relief from his afflictions, speak about them or question His ways).
Ibn Ezra: One should not say Piyutim that he does not understand. Perhaps the author, or those who copied the words, erred. One should say only the fixed Tefilah, and he will not be punished.
Why should one say few words in front of Hashem?
Rashi (2): Lest he stumble amidst many words - "b'Rov Devarim Lo Yechdal Pesha" (Mishlei 10:19). Rashbam - anyone who increases words, he brings sin (Avos 1:17).
Ibn Ezra: It is lest he be in danger. On Yom Kipur, the Kohen Gadol said a short Tefilah [in the Heichal], and left.
Seforno: Perhaps you will veer from the proper intent, and sin.
Metzudas David: Amidst many words, you will come to complain against Hashem's decree.
