ולעבדו בכל לבבכם, "and to serve Him with all your hearts.⁠" Our sages in Taanit 2 ask rhetorically: "what kind of service can one perform for God with one's heart?⁠" They answer: "Prayer.⁠" They prove this from Daniel 6,17: "your God, the one whom you serve constantly, He will save you.⁠" Was there then a Temple for the Jewish God in Babylon where Daniel could have offered sacrifices? Clearly the King must have referred to the God to whom Daniel prayed in his heart. In verse 11 of that same chapter Daniel is described as opening the window of his room facing Jerusalem when praying. David also said in Psalms 141,2: "take my prayer as an offering of incense.⁠" Moreover, our sages in Berachot 26 have said that the daily prayers nowadays are in lieu of the daily communal offerings, the תמידים.

It is important to appreciate that the power of prayer is such that it can bring about changes in the laws of nature, save people from mortal danger, and bring about cancellation of evil decrees by God. We know that it can effect changes in the laws of nature from Yitzchak whose prayer in the presence of Rivkah brought about the new-found ability of Rivkah to conceive (Genesis 25,21). She had previously been barren, and our sages explain that this was so as God wanted to encourage Yitzchak to pray to Him to reverse this situation. (compare Shir Hashirim Rabbah 2,31). Our sages explained to us that the barrenness of our matriarchs was due only to the absence of the prayers of either themselves or their husbands.
Proof that prayer can save one from mortal danger is found in Psalms 107,23: "the ones who descend to the sea in ships.⁠" We know that from when Jonah prayed inside the fish, surely a mortal danger if ever there was such. Not only this, but David continues in that psalm describing how the mariners in time of a storm pray to God Who saves them from these dangers. As a result of their prayers God silences these turbulent waters (verse 29).
Proof that prayer is able on occasion to reverse evil decrees by God is found in Isaiah 38,8 where God tells King Chizkiyah that his prayer has been granted that he will enjoy a 15 year extension of his lifespan after the prophet had told him in the name of God to make his last will and testament as he would not recover from his sickness. (Compare Berachot 10 on what the king told the prophet.) The Talmud tells us not to despair even if the sword is poised to fall on one's neck, that God is still able to help. They quote Job 13,15 to prove their point. Incidentally, our sages there reveal that the power of prayer exceeds the power of prophecy.
In this connection we must remember that in the period between Moses and the men of the Great Assembly (over 900 years later) prayer was not formalized as it is nowadays. Every person formulated his prayers in his own words in accordance with his knowledge and ability. The men of the Great Assembly organised the formula which serves until this day as the principal prayer commonly known a the Shmone Esreh, ("18,⁠" according to the number of benedictions which it contains). The main reason the men of the Great Assembly formulated this prayer was to ensure that everyone would learn it by heart and be familiar with it. This is why the language of that prayer is very plain and simple.
This would prevent people from becoming confused and making errors. The sages wanted the prayers of both fools and wise men to be identical so that the fools would not feel at a disadvantage.
These benedictions were composed with the utmost care and with regard to such formulas having proved successful. The introductory benediction, known as אבות introduces the petitioner as a descendant of the patriarchs and as such entitled to a hearing. It is followed by a benediction known as גבורות, a declaration of our awareness of God's mighty deeds. The third benediction is called קדושה, a prayer in which we extol God's Holiness. These three benedictions are followed by a string of בקשות, requests (12 in all) which are arranged both in terms of our spiritual needs, our physical needs, our national needs and our individual needs. The final three benedictions consist of עבודה, a prayer asking for the restoration of the Temple and the sacrificial service in the Temple, followed by a benediction known as הודאה, thanksgiving. This is followed by the blessing by the priests, the prayer for peace, without which all the other blessings are short-lived.
If you will examine the letters in the tetragrammaton י-ה-ו-ה you will find that if the letters of that name are spelled in a different sequence you have a total of 12 variations, known as צירופים, permutations. An example of these variations is that starting with the first letter י you could follow it with either a ו followed by two letters ה, or by the letter ה twice followed by the letter ו. The three basic letters in the tetragrammaton, the letters י-ה-ו lend themselves to six permutations, i.e. יהו,יוה,הוי,היו,ויה,והי giving you a total of 6 such צירופים. The tetragrammaton, having four basic letters, doubles the number of permutations possible so that you wind up with basically 12 צירופים. [Some authorities speak about 24. Ed]. The number 12 corresponds to the numerical value of the word זה in the verse זה שמי לעולם, "this is My name forever" (Exodus 3,15). The three first permutations, i.e. the ones using the letter י at the beginning, correspond to the first three of the benedictions representing אבות, גבורות, קדושה. The final three צירופים in that series correspond to the last three benedictions עבודה, הודאה, ברכת כהנים. The 6 permutations in the middle correspond to six of the 12 central requests, i.e. אתה חונן, השיבנו, סלח לנו, גאולה, רפואה, פרנסה. The other six benedictions do not have a specific permutation of the tetragrammaton assigned to them and one can perceive them as being used interchangeably. The reason that the 19th benediction, the one added by later sages as a request to ward off the potential damage caused to Jews and Judaism by its defectors and maligners cannot be assigned any of these permutations of the tetragrammaton is that this benediction is addressed in the first instance to the attribute of Justice, not the tetragrammaton as we want that attribute to neutralize these anti Jewish forces.
This nineteenth benediction and its significance has already been alluded to in Psalms 29 where after mentioning the tetragrammaton 18 times, David adds the words ואל הכבוד הרעים, in verse 3, a reference to the attribute of Justice. The only reason David changes the attribute he addresses there after having referred to the tetragrammaton 18 times is that he hints that this attribute ought to be poised, ready to strike these virulent anti-Semites unless they retract.
Another reason that David introduces an additional attribute of God in that psalm is that he conveys the message that not only our external enemies but our internal enemies, the evil urge, should be taken care of by the attribute of Justice. We encourage the attribute of Justice, so to speak, to vent its anger on our internal enemies.

Among the 12 requests we observe that 6 address human needs whereas the other 6 are the plea for the restoration of God's kingdom on earth and His closeness to His people as it had been prior to the destruction of the Temple. By means of the addition of the 13th request, the one to liquidate the hostile heretics, we have a total number of 13 requests corresponding to the 13 attributes of Himself which God revealed to Moses after the episode of the golden calf. This is an allusion to the fact that all the good on earth, be it for the benefit of man or God Himself, is channeled our way by means of these attributes in one form or another. It is therefore incumbent upon us to address the Essence of God, Who operates by means of these attributes. This is what Moses had in mind when he quoted the Gentile nations (Deut. 4.7) as describing our relationship to that Essence as אשר לו אלו-הים קרובים אליו. The Gentiles felt that no other nation established such a close relationship to the Divine Essence, the tetragrammaton, by means of the attributes as did the Jewish people. This is conditional on בכל קראנו אליו, "providing that when we pray we always call out to Him, the Essence" (Deut. 4,7). The word אליו specifically excludes any of the attributes as being the address to which our prayers are to be directed.