The Quran

Preface

إِنَّمَا النَّسيءُ زِيادَةٌ فِي الكُفرِ ۖ يُضَلُّ بِهِ الَّذينَ كَفَروا يُحِلّونَهُ عامًا وَيُحَرِّمونَهُ عامًا لِيُواطِئوا عِدَّةَ ما حَرَّمَ اللَّهُ فَيُحِلّوا ما حَرَّمَ اللَّهُ ۚ زُيِّنَ لَهُم سوءُ أَعمالِهِم ۗ وَاللَّهُ لا يَهدِي القَومَ الكافِرينَ

Yusuf Ali

Verily the transposing¹ (of a prohibited month) is an addition to Unbelief: the Unbelievers are led to wrong thereby: for they make it lawful one year, and forbidden another year, in order to adjust the number of months forbidden by God and make such forbidden ones lawful. The evil of their course seems pleasing² to them. But God guideth not those who reject Faith.

To meddle with an old-fashioned custom of close time for warfare during Prohibited or Sacred Months was not only a demonstration of the Unbelievers against the Muslims on account of their Faith, but was wrong and unjust in itself, as it abolished a wholesome check on unregulated warfare, and prejudiced the law-abiding side by arbitrary decisions.
Cf. 6:122. The lawless man thinks he is doing a great thing in getting the better of those who are careful to observe a law they believe in. But the lawless man loses the guidance of Faith, which is a symbol of his being guided by God; he will therefore lose in the end.