On this topic, Rav Shimshon Pinkus zt"l (Sefer Tiferes Shimshon) says as follows:
Chazal describe the extent of the tefillos of Moshe Rabenu to be allowed to enter the land. They say (Devarim Rabbah 11:10) that he donned sackcloth and coated himself with ashes. He then stood in prayer and supplication before Hashem until the Heavens and earth and the entire order of creation shook.
Hashem then issued a proclamation to every gate of Heaven and to every Heavenly court not to allow the prayers of Moshe to enter and not permit them to ascend to Him because the decree had already been sealed. Hashem called all the ministering angels and told them, "Hurry and close every gate to Heaven because the sounds of his prayers are strongly pushing upwards and are trying to ascend." His prayers were like a sword that cuts through everything in its path. They were like the "Shem Hameforesh" that he had learned from the Divine beings.
The Medrash concludes: At that time, Hashem said, "I heard from behind Me the sound of a ra'ash gadol (great commotion, Yechezkel 3:12)." And 'ra'ash' always means "zeya" (exertion). And there is no "gadol" like Moshe, as is stated (Shemos 11:3): "This man, Moshe, is very 'gadol' in the land of Egypt, in the eyes of Pharaoh and in the eyes of the nation."
When we contemplate the greatness of the prayers of Moshe Rabenu, it is important to note the words of the Zohar Hakadosh (Parshas Balak, 195A). It states that there are three types of tefillos: "Tefillah L'Moshe", "Tefillah L'Dovid" and "Tefillah L'Ani". The loftiest of the three is "Tefillah L'Ani" (the prayer of a poor man) because a poor man davens with a broken heart, and it is stated (Tehillim 34:19) that Hashem is close to the brokenhearted and He hears his words. Therefore, when a poor man prays, all the windows of Heaven are opened for him.
These words are unbelievable! Moshe Rabenu's tefillos were on the level of the 'Shem Hameforash' and they were able to cut through the Heavens like a sword, but the tefillos of a poor man who davens with a broken heart are even greater! Therefore, one must always be careful not to wrong a poor man, lest he daven to Hashem against you, as his prayers are always heard.
He concludes: "In general, the best advice for a good, fortunate life is for a person to act like a poor man before Hashem by praying with a broken heart. Through this, the windows of Heaven will open for him and he will be showered with much blessing, success and Divine assistance."
