Chastising the Hypocrites
Ayah 61 tells us that turning away from the decision of the Prophet sallAllahu aalyhi wa sallam, given under the dictates of the Shariah in matters relating to mutual quarrels and disputes, can never be the response of a Muslim. One who does it has to be a munafiq (hypocrite).
Thus, when the disbelief of this hypocrite was practically exposed through his dissatisfaction with the decision of the Prophet sallAllahu aalyhi wa sallam, his being killed by Umar radhi Allahu anhu became all the more justified, because he no more remained a munafiq (hypocrite) and, in fact, became an open Kafir (or apostate). Therefore, it was said in ayah 61,
وَإِذَا قِيلَ لَهُمْ تَعَالَوْاْ إِلَى مَآ أَنزَلَ اللَّهُ وَإِلَى الرَّسُولِ رَأَيْتَ الْمُنَـفِقِينَ يَصُدُّونَ عَنكَ صُدُوداً
“And when it is said to them, ‘Come to what Allah has revealed, and to the Messenger’, you see the hypocrites turning away from you in aversion.”
This shows that the hypocrites used to bring only such cases before the Prophet sallAllahu aalyhi wa sallam as were likely to be decided in their favor, but would refrain from bringing such cases, which they feared, would be decided against them. The same is true of many hypocrites of today: they are ever ready to submit to the decisions of the Islamic Law if and whenever it goes in their favor; otherwise they resort to any law, any custom, and any law court which, they expect, will ensure their interests.