The speech in this Surah is directed to the Prophet Muhammad (saws). This shows the Prophet’s (saws) honesty in the duty of notification from Allah (swt).
Verify, reciting the Holy Qur’an is a form of worship, in every single letter of it.
الْكَافِرُونَ (disbelievers): They are specifically a section of disbelievers, whom Allah (swt) had known that they will never believe, they are the masters of polytheism in Mecca.
Those people are in one side and the Prophet (saws) in on the opposite one.
يَا أَيُّهَا (O’): This form of calling is used for a distant one. It is used to express either an extra degree of respect or contempt, because being distant has two indications, either a high rank and far status at Allah (swt) or a low rank and far status from Allah (swt).
Thus, when Allah (swt) addresses His Prophet (saws) by:
﴾يَا أَيُّهَا النَّبِيُّ﴿
(O Prophet,..) (Al-Anfal: 64)
﴾ يَا أَيُّهَا الرَّسُولُ﴿
(O Messenger,,..) (Al-Maaidah: 41)
These two callings here carry the meaning of superior status and position and they are on the contrary of the calling in the verse we are explaining.
However, the Prophet (saws) went to the disbelievers gathering and announced to all this verse which represents a cut-off of the relation connected with worship.
Allah (swt) does not say (O you who disbelieved) because they were not believers before that, rather they were engaged in disbelief from the first beginning.
As the Arabic word of disbelief means covering, this illustrates the instinct of faith, which is the covered.