Connecting the Concept with the Alter Rebbe's Teachings
We can connect all of this with that which the Alter Rebbe explains in Likkutei Torah regarding the statement: “The term ‘וָאֶתְחַנַן’ is nothing but a request for a ‘free gift’”. That through his entry into Eretz Yisroel (about which Moshe pleads: וְאֶרְאֶה וְגוֹ׳ אֶעְבְרָה־נָא “Pray let me cross over and see”) Moshe Rabeinu wanted to bring up the B’nei Yisroel to a spiritual level that they would not otherwise be able to attain through their own efforts. This symbolises an Isarussa Dil’eilah which is way beyond the reach of an Isarussa Diletatoh. This is the meaning of the term ‘Matnas Chinom’ as in ‘free - without Mitzvos’, hence a spiritual level beyond Mitzvos.
With this we can explain the rationale of the Sifri when he says that ‘וָאֶתְחַנַן’ is not one of the ten expressions of prayer. This is because prayer is an Avodah that one operates from his own efforts down below with ‘Isarussa Diletatoh’.
Therefore, in order to have Hakodosh Boruch Hu fulfil Moshe’s request of אֶעְבְרָה־נָא וְאֶרְאֶה וְגוֹ׳ “let me cross over and see,” that would have caused a Divine revelation in the manner of an Isarussa Dile’eilah to have an effect on the B’nei Yisroel, he needed to make his request in this same vein. In other words, to request (not in a manner of prayer which is connected with his merits, but in a manner of) pure ‘Matnas Chinom’ that is not connected with any merits etc.
However, the Medrash Rabbah holds that ‘וָאֶתְחַנַן’ is one of the ten expressions of prayer. This will be better understood through the prism of that which it says in Likkutei Torah, that Moshe’s above-mentioned request (That the ‘Isarussa Dile’eilah’ which transcends the ‘Isarussa Dile’tatoh’ shall be revealed) is a part of Torah because through it the state of ‘I am who I am’ is drawn down into this world which is a much higher level than ‘Isarussa Diletatoh’ and does descend as a gift.
