Spiritual bounty often leads to strife; Our fallen nature tends to evil and resents the good that requires it to change, mature, and grow. It is not surprising therefore to see the Passover followed by petty complaints and jealousy.
The first complaint is about misfortunes, but the complaint is not one of trust but distrust. God's anger flares and consumes the outlying parts of the camp. Then, the people cried to Moses who interceded on their behalf and the fire stopped. So often do we go to God with a list of complaints or requests, treating him like a solution-maker or a Santa Klaus, and when he does not answer our petitions according to our expectations, we become confused and look around for someone to help us.
Thankfully, God does not leave us alone, for even when we are seeking him the wrong way, he responds by sending an intercessor our way, someone who can help and guide us: a saint, a priest, a religious, pious, and wise friends. He does not leave us alone.
Even when we fall into jealousy as Miriam did when she thought to elevate herself and become equal to Moses. God showed her wretchedness through leprosy and taught her a lesson of trust and humility by allowing Moses to intercede on her behalf. So it is in our case, God sends us a sickness that affects our bodies to save us from the danger of self-love and the illusion of strength and control we like to bask in. But he does not leave us alone, sending us an intercessor to guide us back home.