מי יתן והיה לבבם זה להם ליראה אותי, "who can assure that their heart should remain the same for them to revere Me, etc.⁠" According to the plain meaning of the text the reason that Moses quoted God as using the words מי יתן, "who could assure?⁠" is that seeing that God had divested Himself of the right to control man's heart by granting him free will, there is no authority in the world which could guarantee that His wish be fulfilled. This is why our sages in Berachot 33 coined the phrase "all is within the power of heaven except the fear of heaven.⁠"

A Midrashic approach (based on Midrash Tehillim 14): We must understand these words in the same vein as Psalms 14,7: מי יתן מציון ישועת ישראל, "O that the deliverance of Israel might come from Zion!⁠" David records this same verse twice in the Book of Psalms (compare Psalms 53,7). Why did he do so? The verses have to be understood as respective wishes by teacher and student. The teacher expresses the wish that the students would remain on their spiritual high as evidenced at the time of the revelation at Mount Sinai, whereas the student (Moses) expresses a similar wish regarding the teacher, i.e. מי יתן כל עם ה' נביאים, "who could assure that God's entire nation were gifted with the power of prophecy!⁠" (Numbers 11,29 when Eldad prophesied and Joshua was upset.) The fact is that in this terrestrial world there is no assurance that either the wish of the "teacher" or the wish of the "student" will be fulfilled. In fact, according to the Midrash it is certain that the wishes of both will not be fulfilled. However, in the life after the arrival of the Messiah the psalmist is convinced that such wishes will be fulfilled. He bases himself on Ezekiel 36,26 who describes the ushering in of that age with God's promise to replace the heart of stone with a heart of flesh. This will result in the wishes of the teacher regarding the conduct of his pupil being fulfilled. He also finds an allusion to the wishes of the pupil being fulfilled in that new world in the prophecy of Yoel 3,1: "l will pour out My spirit upon all flesh.⁠" The reason David repeated this verse then is to teach us that the time will come when both these types of wishes will become realistic and subject to realization.

A kabbalistic approach: The words מי יתן והיה לבבם זה, "these words were uttered by Hashem, meaning who would "inspire" the emanation of wisdom, the source of inspiration for reverence of the Lord, to be active in this regard on an ongoing basis!. Seeing that God has to wish that the emanation "wisdom" do or not do certain things is proof that God Himself is unable to do this. This is the true meaning of the statement by the sages we quoted that "all is in the hands of heaven except the fear of heaven.⁠" The sages referred to the attribute known as heaven, an attribute which has great powers but whose powers do not include the ability to inculcate fear of the Lord in people. It is something "beyond" this particular attribute, emanation, as it has no control over inspiring reverence for God in people.
We find a dialogue between Moses and the people described in Avodah Zarah 5 where Moses is described as having harangued the Israelites for being ungrateful when they heard God express the wish that the people should always be on a spiritual high such as they attained at Mount Sinai. According to Moses they should immediately have asked God to grant that His own wish be fulfilled. Surely this dialogue described in the Talmud presupposes that God does have control over who would and who would not possess יראת שמים, "reverence for heaven!⁠" Moses meant that the people should have asked God to address His prayer to an emanation higher than the one called שמים.
This reflects something we learned in Taanit 25 in connection with Rabbi Eleazar ben Pedot who was in very depressed economic circumstances and it bothered him so that God asked him if he really wished that God should decree destruction on earth so that possibly on his next round of life he might be born under a more propitious horoscope? Rabbi ben Pedot was amazed to learn that even if God were to turn the universe upside down on his account this would still not be a guarantee that his personal fortunes would improve significantly. He therefore declined the "offer.⁠" [The author mentioned only the gist of the story, and although I added some of what is found in the Talmud I suggest to the interested reader to read the whole story in the Talmud. Ed.].
In a different context the Talmud tells the story of how God showed Moses all the leaders of successive generations including that of Rabbi Akiva and his death through cruel torture by the Romans. When Moses saw with his mental eye that Rabbi Akiva's flesh was being offered for sale in the store, he exclaimed: "is this the reward you receive for excelling in Torah?⁠" God told Moses to keep silent, that He had seen fit to allow things to happen this way. (Compare Menachot 29 and Nachmanides' comment).
The meaning of this comment by God (speaking as the essence) there is that the emanation "wisdom" decreed to delay punishment for the crime of the sale of Joseph by his brothers until over 1200 years later for the sake of the Jewish people as a whole. You find a comment in Midrash Rabbah on the first half of Proverbs 8,30 ואהיה אצלו אמון, "I was like an artisan with Him,⁠" explaining these words as meaning that the Torah says about God that it was God's artisan, i.e. He used it to fashion the world. Just as the King when he builds a palace does not do so with his own hands but employs the services of an architect, but the architect works according to plans provided by the king, not making his own designs, so God "looked" into the Torah to consult how best to implement His own plans for the universe. Thus far the Midrash.
The meaning of all this is that the author of the Midrash compared the Shechinah to a king of flesh and blood and His great name to the "artisan" who carries out the various tasks assigned to him by God's essence The חכמה, the emanation wisdom, is perceived as the textbook which serves the artisans as a standby for consultation to perform their work in the most efficient manner. This is why Moses of whom the Torah wrote in Deut 33,21 וירא ראשית לו כי שם חלקת מחוקק ספון, "he chose the first portion for himself for that is where the lawgiver's plot is hidden,⁠" was called מחוקק. [The reason this needs explaining is that this term normally translated as "lawgiver" suggests that the law is initiated by such a מחוקק. This would mean that Moses acted independently of God, an intolerable thought. The Midrash therefore introduces these parables to define Moses' role within the hierarchy commencing at the top with God the essence, the emanation wisdom, the Torah as the textbook of wisdom, etc. Ed.] The Talmud elsewhere defines this word as similar to parchment which has been salted and treated with flour in order to make it ready for the writing on it to endure.
We encounter such Midrashim (Tanchuma Va'eyra 5) in connection with Pharaoh, who, when told by Moses that he was sent by Hashem, is reported to have asked his magicians to take out all the books containing the names of any past and present deities to search for the name Hashem. The Midrash refers to these "books" also as דפתרא, the kind of parchment we just described. All of this merely proves that the king does not proceed to implement his plans without going "through channels.⁠" When we keep this in mind we do not find some of our sages' statements as so difficult to comprehend. Seeing that an artisan is not a robot and does not perform his work mechanically without employing his mental faculties it becomes clear that חכמה, the emanation wisdom, is pivotal to all of God's activities. This then is the mystical dimension of Job 28,28: "See, fear of the Lord is wisdom,⁠" i.e. "wisdom, i.e. pure intelligence, pure thought equates with reverence of the Lord the Creator, the master of the universe.⁠" This is also the mystical dimension of Isaiah 30,18: ולכן יחכה ה' לחננכם ולכן ירום לרחמכם, "truly, the Lord is waiting to show you grace, truly, He will arise to pardon you.⁠" Why does the prophet switch from the verb חכה in the first half of the verse to רום in the second half of the same verse? The first half of the verse describing God as waiting is similar to the wish expressed by God in our verse here where God waits for the Jewish people to maintain their spiritual high. The second part, i.e. the word ירום describes the result of such waiting at the end of which time God can endow the people with His חכמה. חכמה and אמונה, "wisdom and faith" are so closely interwoven as to make them almost inseparabable.

The author, quoting the Kabbalist Rabbi Yitzchok ben Harav suggests that psalm 143,1 באמונתך ענני בצדקך, is to be understood as an oath to which David wants God to commit Himself.