And remember the Name of your Lord and (Tabattal) devote yourself to Him with complete devotion.
meaning, make much remembrance (Dhikr) of Him, devote yourself to Him and spend your time worshipping Him when you have completed your occupations and what you need from the affairs of your worldly matters. This is as Allah says,
فَإِذَا فَرَغْتَ فَانصَبْ
So when you have finished (your occupation), devote yourself for Allah's worship. (94;7)
meaning, when you have completed your tasks and occupations, then busy yourself in His obedience and His worship so that you will have free time for leisure.
The meaning of this was said by Ibn Zayd, or close to its meaning.
Ibn `Abbas, Mujahid, Abu Salih, `Atiyah, Ad-Dahhak and As-Suddi, all said,
وَتَبَتَّلْ إِلَيْهِ تَبْتِيلً
And (Tabattal) devote yourself to Him with complete devotion.
"This means, make your worship solely for Him alone."
Al-Hasan said, "Strive and devote yourself to Him."
Ibn Jarir said,
"A devout worshipper is called Mutabattil. An example of this is the reported Hadith that he (the Prophet ) forbade At-Tabattul, which means total devotion to worship while avoiding getting married."
Allah said,
رَبُّ الْمَشْرِقِ وَالْمَغْرِبِ لَا إِلَهَ إِلاَّ هُوَ فَاتَّخِذْهُ وَكِيلً