Quran: Surat al-Baqara (the Cow) verses 216-218: Quran Tafsir(Commentary on) Ibn Kathir - Jihad is made Obligatory
In this Ayah, Allah made it obligatory for the Muslims to fight in Jihad against the evil of the enemy who transgress against Islam. Az-Zuhri said, "Jihad is required from every person, whether he actually joins the fighting or remains behind. Whoever remains behind is required to give support, if support is warranted; to provide aid, if aid is needed; and to march forth, if he is commanded to do so. If he is not needed, then he remains behind.''
On the day of Al-Fath (when he conquered Makkah), the Prophet said:
There is no Hijrah (migration from Makkah to Al-Madinah) after the victory, but only Jihad and good intention. If you were required to march forth, then march forth.
(...though you dislike it) means, `Fighting is difficult and heavy on your hearts.' Indeed, fighting is as the Ayah describes it, as it includes being killed, wounded, striving against the enemies and enduring the hardship of travel. Allah then said:
. ..and it may be that you dislike a thing which is good for you) meaning, fighting is followed by victory, dominance over the enemy, taking over their lands, money and offspring. Allah continues:
(...and that you like a thing which is bad for you.)