Allah says:

وَأَقْسَمُوا بِاللَّهِ جَهْدَ أَيْمَانِهِمْ لَئِنْ أَمَرْتَهُمْ لَيَخْرُجُنَّ ...

They swear by Allah their strongest oaths that if only you would order them, they would leave.

Allah says about the hypocrites who had promised the Messenger and sworn that if he were to command them to go out for battle, they would go:

... قُل لَّا تُقْسِمُوا ...

Say: "Swear you not...''

meaning, do not swear this oath.

... طَاعَةٌ مَّعْرُوفَةٌ ...

obedience is known.

It was said that the meaning is, your obedience is known, i.e., it is known that your obedience is merely verbal and is not accompanied by action. Every time you swear an oath you lie.

This is like the Ayah:

يَحْلِفُونَ لَكُمْ لِتَرْضَوْاْ عَنْهُمْ

They swear to you that you may be pleased with them... (9:96)

And Allah says:

اتَّخَذْواْ أَيْمَـنَهُمْ جُنَّةً

They have made their oaths a screen (for their evil actions). (58:16)

It is part of their nature to tell lies, even in the issues they choose, as Allah says:

أَلَمْ تَرَ إِلَى الَّذِينَ نَـفَقُواْ يَقُولُونَ لإِخْوَانِهِمُ الَّذِينَ كَفَرُواْ مِنْ أَهْلِ الْكِتَـبِ لَئِنْ أُخْرِجْتُمْ لَنَخْرُجَنَّ مَعَكُمْ وَلاَ نُطِيعُ فيكُمْ أَحَداً أَبَداً وَإِن قُوتِلْتُمْ لَنَنصُرَنَّكُمْ وَاللَّهُ يَشْهَدُ إِنَّهُمْ لَكَـذِبُونَ

لَئِنْ أُخْرِجُواْ لاَ يَخْرُجُونَ مَعَهُمْ وَلَئِن قُوتِلُواْ لاَ يَنصُرُونَهُمْ وَلَئِن نَّصَرُوهُمْ لَيُوَلُّنَّ الاٌّدْبَـرَ ثُمَّ لاَ يُنصَرُونَ

Have you not observed the hypocrites who say to their friends among the people of the Scripture who disbelieve: "If you are expelled, we indeed will go out with you, and we shall never obey any one against you; and if you are attacked, we shall indeed help you.'' But Allah is Witness that they verily are liars.

Surely, if they are expelled, never will they go out with them; and if they are attacked, they will never help them. And if they do help them, they will turn their backs, and they will not be victorious. (59:11-12)

... إِنَّ اللَّهَ خَبِيرٌ بِمَا تَعْمَلُونَ ﴿٥٣﴾

Verily, Allah knows well what you do.''