Imam Khomeini has undertaken very insightful discussions in this regard in his book "discipline of prayers".
According to Imam, Our Salats which are not accompanied by submission are caused by a deficiency of faith or by lacking it.
Belief [i'tiqād] and knowledge are other than faith, our knowledge of Allah, His Names and Attributes and of other divine knowledge [ma'ārif], is other than faith.
Satan according to the testimony of Allah, has information about the Beginning and the Resurrection, yet, he is a disbeliever. He said:
“You have created me of fire, while You created him of dust.”
So, he believes in Allah and in His being the Creator; and he says: “Respite me until the day they are resurrected.”
So, he believes in the Day of Resurrection, too. He knows about the Books, the Messengers and the angels. Nevertheless, Allah addresses him as a disbeliever, excluding him from the group of the believers [mu'minīn].
Thus, the people of knowledge are distinct from those of faith. Not every man of knowledge is a man of faith.
Therefore, after acquiring knowledge, one has to join the believers, and to convey the Greatness, Majesty, Brightness and Beauty of Allah, the Most Exalted and High, to his heart, so that it may become submissive, since mere knowledge does not result in submission, Imam further explained.
You can realize it in yourself: although you do believe in the Beginning and the Resurrection and in Allah's Majesty and Glory, your heart is not submissive.
As to Allah's saying:
“Has not the time yet come for those who believe that their hearts should be submissive when remembering Allah and what has come down of the truth,”
it may be that it is the formal faith the very belief in what the Prophet (PBUH) has brought which is intended here, for the true faith is accompanied by a degree of submission; or the submission in the noble āyah may refer to a submission at its complete degree, as sometimes they apply the word, ‛ālim(erudite) to the one whose knowledge has reached the limit of faith.
In the noble āyah:
“…verily only the erudite among Allah's servants fear Him.”
Read more:
Imam Khomeini paved long way for self-purification