Hypocrites are barred from participating in Jihad
Allah commands His Messenger, peace be upon him,
فَإِن رَّجَعَكَ اللَّهُ
(If Allah brings you back), from this battle,
إِلَى طَآئِفَةٍ مِّنْهُمْ
(to a party of them) in reference to the twelve (hypocrite) men, according to Qatadah,
فَاسْتَأْذَنُوكَ لِلْخُرُوجِ
(and they ask your permission to go out), with you to another battle,
فَقُلْ لَّن تَخْرُجُواْ مَعِىَ أَبَدًا وَلَن تُقَـتِلُواْ مَعِىَ عَدُوًّا
(say: "Never shall you go out with me nor fight an enemy with me...") as an admonishment and punishment for them. Allah mentioned the reason for this decision,
إِنَّكُمْ رَضِيتُمْ بِالْقُعُودِ أَوَّلَ مَرَّةٍ
("You were pleased to sit (inactive) on the first occasion...") Allah said in a similar Ayah,
وَنُقَلِّبُ أَفْئِدَتَهُمْ وَأَبْصَـرَهُمْ كَمَا لَمْ يُؤْمِنُواْ بِهِ أَوَّلَ مَرَّةٍ
(And We shall turn their hearts and their eyes away (from guidance), as they refused to believe therein for the first time. ) 6:110 The recompense of an evil deed includes being directed to follow it with another evil deed, while the reward of a good deed includes being directed to another good deed after it. For instance, Allah said concerning the `Umrah of Hudaybiyyah,
سَيَقُولُ الْمُخَلَّفُونَ إِذَا انطَلَقْتُمْ إِلَى مَغَانِمَ لِتَأْخُذُوهَا
(Those who lagged behind will say, when you set forth to take the spoils.)48:15 Allah said next,
فَاقْعُدُواْ مَعَ الْخَـلِفِينَ
("...then you sit (now) with those who lag behind.") in reference to the men who lagged behind from Tabuk battle, according to Ibn `Abbas.
Tafsir Ibn Kathir (abridged, English).