Quran 25:52 – “Therefore listen not to the Unbelievers, but strive against them with the utmost strenuousness…”
The words used, ‘strive against them’, means, striving to preach the Quran. To call people to Islam using the Quran. The passage does not endorse violence against the innocent.
Tafsir Ibn Kathir
(So obey not the disbelievers, but strive hard against them with it.) meaning, with the Qur’an. This was the view of Ibn `Abbas. 
So do not obey the disbelievers, in their desires, but struggle against them therewith, that is, through [adherence to] the Qur’ān, with a great endeavour. 
The Holy Qur’an Arabic Text With English Translation & Short Commentary – Malik Ghulam Farid
2084. The great and real Jihad, according to this verse, is to preach the Message of the Qur’an. Thus to strive for the propagation of Islam and the dissemination and diffusion of its teachings is the jihad which the Muslims are enjoined always to carry on with unabated zeal. It is this jihad to which the holy prophet referred when, on returning from an expedition, he is reported to have said: ‘We have returned from the smaller Jihad to the greater Jihad (Radd al-Muhtar). 
The Holy Quran Arabic Text with English Translation, Commentary and comprehensive Introduction – Maulana Muhammad Ali
52a. This verse affords a cler proof of the significance of the word Jihad, as used in the Holy Qur’an. Every exertion to spread the Truth is, according to this verse, a Jihad; nay, it is called the Jihad Kabir (‘mighty striving’) or the great Jihad. Fighting in defence of religion received the name Jihad, because under the circumstances it became necessary for the Truth to live and prosper; if fighting had not been permitted,
Truth would surely have been uprooted. The commentators all accept this significance of the word here. It should be noted that the greatest Jihad which Muslim can carry on is one by means of the Qur’an, to which the personal pronoun ‘it’ at the end of the verse unquestionably refers, because it must be carried on by every Muslim under all circumstances. 
However, one of the most important types of Jihad was practiced in early Islam- the summoning of the polytheists by the Prophet (and after him by his Companions) to the truth (bu-da ’wathim ila L-haqq) and their verbal refutation of the practices of the pagan Arabs and their forefathers. Their resoluteness in speaking words of truth to counter wrongdoing, despite the persecution and the hardships that they encountered as a consequence, is also amnd the most important types of Jihad.
Another important component of the Jihad of the early Jihad, al-Buti continues, was their constant engagement with the Book of God and reflection upon it (al-tabsir bi-kitab Allah) and their fearless proclamation of the message contained within it, without any regard for the dangers that consequently engulfed them.
These most important forms of Jihad were set in motion by Qur’an and its proofs and characterizes it as ‘a mighty striving’ (Jihadan Kabiran), indicating its central distinctive nature among the various forms of Jihad.
These various forms of striving that have nothing to do with fighting constitute the foundation and essence of Jihad, as further indicated in the aforementioned Qur’an 16:110, a Meccan verse with the exhortation to ‘strive and be steadfast,’ which must be understood in this non-combative sense.
Hadiths, such as the one in which Muhammed says, ‘The best Jihad is a word of truth before a tyrannical ruler’ and ‘the best Jihad is your striving against yourself and desires for the sake of God Almighty,’ provide further corroboration of these non-combative significations, continues our author. 
Quran Translation and Commentary – Maulana Mufti Mohammad Shafi
JIHAD WITH QUR’AN (ITS PROPAGATION) IS GREAT JIHAD
(And strive against them with it (the Quran) a great striving 25:52). What is ordained in this verse is that you spread the message of Qur’an among the people at large. 
 Tafsir Ibn Kathir – http://www.study-quran.com/2013/02/tafsir-ibn-kathir-qs-at-taubah-73-74.html”>http://www.study-quran.com/2013/02/tafsir-ibn-kathir-qs-at-taubah-73-74.html
 Tafsir al-Jalalayn – http://www.altafsir.com/Tafasir.asp?tMadhNo=0&tTafsirNo=74&tSoraNo=25&tAyahNo=52&tDisplay=yes&UserProfile=0&LanguageId=2
 The Holy Qur’an Arabic Text With English Translation & Short Commentary by Malik Ghulam Farid page 739
 The Holy Quran Arabic Text with English Translation, Commentary and comprehensive Introduction [Year 2002 Edition] by Maulana Muhammad Ali page 725
 Striving in the Path of God: Jihad and Martyrdom in Islamic Thought By Asma Afsaruddin page 246
 Quran Translation and Commentary by Maulana Mufti Mohammad Shafi page 495