"Indeed, We are sending the she-camel" means: bringing her forth, "as a trial for them" means: as a tribulation. "So watch them" means: wait to see what they will do, "and be patient" regarding what they do and what they say; that is, when the she-camel arrives. The explanation of the affair of the she-camel has already passed in Surat al-Shu'ara'.
﴿إِنَّا مُرْسِلُوا النَّاقَةِ﴾ أَي: مخرجوها ﴿فتْنَة لَهُم﴾ أَي: بلية ﴿فارتقبهم﴾ أَي: انظرْ مَاذَا يصنعون ﴿وَاصْطَبِرْ﴾ على مَا يصنعون وعَلى مَا يَقُولُونَ، أَي: إِذا جَاءَت النَّاقة. وَقد مضى تَفْسِير أَمر النَّاقة فِي سُورَة الشُّعَرَاء
