Shaikhul-Islam Ibn Taymiyyah has mentioned this is his essay, 'al-Ubodiyah,' and he also writes,
"Thus, the Deen of Allah is worship, obedience and submission to Him. As for Ibadah, its original meaning also denotes lowliness and submission. One says, 'a pathway that is mu'abbad,' i.e. it has become smoothed out because of being treaded upon. However, the Ibadah that has been enjoined (upon us) encompasses the meaning of submission along with the meaning of love. It embodies the utmost degree of submission to Allah through utmost degree of love to Him...
One who submits to a person whilst possessing hatred for him is not an aabid (worshipper) of him and if he was to love someone and at the same time does not submit to him, he is likewise not an aabid of him as is the case of a man who loves his child and friend.
Consequently, only one of the two (qualities) is not sufficient as far as the Ibadah of Allah is concerned. It is necessary that Allah be the most beloved -above all else -to the abd (the slave) and he should hold Allah to be the greatest of all. Indeed none other than Allah deserves total love and submission...” [end quote] [See, Majmoo at-Tawheed an-Najdiyah, p.549]
Allamah Ibnul-Qayyim (rahimahullah) writes in Nuniyyah:
"Worship of Allah is utmost love for Him,
along with the worshipper's submission,
these are the two axis upon which the orbit of Ibadah
It does not revolve until the axis are established, and
that which causes it to turn is the command of the
Messenger, not desires, soul or Shaytan.”
Allamah Ibnul-Qayyim (rahimahullah) likened the revolution of worship upon love and submission for the beloved (i.e. Allah) -to the revolution of a celestial body upon its axis. He mentioned that the revolution of worship is by the command of the Messenger and what he has ordered -not desire or what the soul or the Shaytan orders him because such would not be worship. So the orders of the Messenger revolves the orbit of worship -not innovations, desires or blind-following of the forefathers."
[end quote from Aqeedah at-Tawheed]