"[Taking] what their Lord has given them," meaning: bestowed upon them in Paradise.
Muhammad said: "Taking" is in the accusative case as a circumstantial qualifier (hal). The meaning is: they are in gardens and springs in the state of taking what their Lord has given them.
﴿آخذين مَا آتَاهُم﴾ أَعْطَاهُم ﴿رَبهم﴾ فِي الْجنَّة.
قَالَ محمدٌ: (آخذين) نصبٌ على الْحَال الْمَعْنى: فِي جناتٍ وعيون فِي حَال أَخذهم مَا آتَاهُم (ل ٨٣٣) رَبهم.
