Then Allah reminds His Prophet the numerous blessings He granted to him and mankind by virtue of sending him to them:

وَمَا كُنتَ تَرْجُو أَن يُلْقَى إِلَيْكَ الْكِتَابُ ...

And you were not expecting that the Book would be sent down to you,

`Before the revelation was sent down to you, you did not expect that revelation would be sent down to you.'

... إِلَّا رَحْمَةً مِّن رَّبِّكَ ...

but it is a mercy from your Lord.

means, `but revelation has been sent down to you from Allah as a mercy to you and to mankind because of you. Since Allah has granted you this great blessing,'

... فَلَا تَكُونَنَّ ظَهِيرًا ...

So never be a supporter, i.e., a helper,

... لِّلْكَافِرِينَ ﴿٨٦﴾

of the disbelievers.

rather, separate from them, `express your hostility towards them and oppose them.'

وَلَا يَصُدُّنَّكَ عَنْ آيَاتِ اللَّهِ بَعْدَ إِذْ أُنزِلَتْ إِلَيْكَ ...

And let them not turn you away from the Ayat of Allah after they have been sent down to you.

meaning, `Do not let their opposition to you affect you or put people off from following your way; do not worry about that or pay any attention to it, for Allah will make your word supreme, will support your religion and will make the Message with which He has sent you prevail over all other religions.'

So He says:

... وَادْعُ إِلَى رَبِّكَ ...

and invite to your Lord,

to worship your Lord Alone, with no partners or associates,