Commentary for Berakhot 57:22

BECAUSE HE CAN RECITE IT IN [THE BLESSING]: WHO LISTENS TO PRAYER. The Gemara says that if one forgot to say “and give dew and rain” during the winter months, he need not repeat the sh’moneh esray because he can insert that prayer in the b’rochoh of שומע תפלה which is a general b’rochoh in which we can ask for any of our needs. As the Gemara says (later 31a, Avodoh Zoroh 8a) a person may ask for his needs during the b’rochoh שומע תפלה. And specifically one’s needs, for example when one has a sick person in his house or his field needs rain which is similar to a prayer and so to asking for dew and rain is a prayer that can be added to שומע תפלה, but declaring that He brings down the rain which is usually recited in the second b’rochoh and havdoloh and other praises of Hashem are not allowed to be said in this b’rochoh because they are not similar to the thought of the b’rochoh of שומע תפלה, which is to pray to Hashem for one’s needs not to declare the greatness of Hashem that he provides these needs on a regular basis.
The Gemara has taught us that שומע תפלה is a general b’rochoh in which one can mention his individual needs. It seems from Tosfos that there were those who thought that this could be taken a step further and when making personal requests from Hashem after the conclusion of the eighteen b’rochos, when we usually say אלקי נצור they would conclude with the words ברוך אתה ה' שומע תפלה.
Tosfos wants to show us that this is totally unacceptable. And it appears that one who says שומע תפלה ברוך אתה ה' after he concludes the words of request while sitting¹It is unclear why Tosfos uses the words “while sitting”. It would seem that this additional b’rocho would be added after the conclusion of personal request while still standing. Perhaps Tosfos means that even if one completed the sh’moneh esray and sat while asking these requests it is also unacceptable even if it does not appear as if he is adding to the sh’moneh esray. is repulsive, as the Gemara says (Megiloh18a) after the Gemara goes through a lengthy exposition explaining the reason for the order of all the b’rochos in sh’moneh esray, after this point, the recital of the final b’rochoh שים שלום, it is prohibited to recite the praises of Hashem, this means, to add b’rochos to these eighteen.
It is clear that it is prohibited to add a b’rochoh to the regular eighteen b’rochos. Tosfos expresses his opinion that even adding an entire sh’moneh esray is forbidden. And even if he comes to pray the entire sh’moneh esray another time and not to only recite one of the b’rochos such as שומע תפלה as we previously discussed, is forbidden, because it appears as if he is adding to the b’rochos of sh’moneh esray.
There is some evidence that addin a second sh’moneh esray is a worthy pursuit. Tosfos deals with that. And that which we said earlier (21a) would that a person pray the entire day, which seems to indicate that it is praiseworthy for one to say sh’moneh esray many times during the day, even more than the three prescribed times that is only when there is a doubt as to whether he prayed or not, he may pray a second time in order to dispel the doubt for even if he prayed already praying again is worthy, but if he definitely prayed, we have said earlier that he must stop even in the middle of a b’rochoh as Shmuel says in perek Mee Shemaiso (ibid.)
But we do find that a person is required to recite the sh’moneh esray twice. And that which we find that the Chazon repeats them, the eighteen b’rochos, that is so that the multitude who cannot say the sh’moneh esray themselves, should fulfill their obligation by listening to the Chazon.
But why must the Chazon first say the sh’moneh esray himself? Why can’t he fulfill his own obligation as he recites it for the congregation? And the reason that the Chazon prays silently together with the congregation, before he recites the sh’moneh esray publicly, that private recital, is in order to put his prayer in order, so that he should be familiar with the text of the prayer when he recites it for the public, as the Gemara says in the last perek of Rosh Hashonoh (34b).

Ibid. p. 49, "Hear our voice."

Ibid. p. 44 bot.

Ibid. p. 216.