The Fruit is obtained from the Flower by subtraction. Within the full overlapping grid, keep the central circle, the six whose centres form the first hexagonal ring around it, and the six lying directly beyond those along the same six directions. Discard everything else. The thirteen circles that remain are the same size as before but no longer overlap: each of the inner six touches the centre circle and its two neighbours, while the outer six touch only one circle each. Where the Flower is a continuous lattice, the Fruit is a discrete arrangement of tangent circles.
Their centres are what matter for what follows. The thirteen centres sit on a triangular lattice (one at the origin, six at one step out, six at two steps along the same axes), and that is why this figure is the hinge of the whole construction sequence. As circles it is a decorative arrangement. As a set of thirteen points it is a coordinate frame, and joining every pair of those points is the operation that produces Metatron's Cube.
Two smaller points are worth making. The figure is drawn sometimes with a hexagonal outline and sometimes inside a circle, and neither is canonical. And these are not the only thirteen circles one could select from the Flower; this particular selection is chosen because of what its centres generate downstream, which is a statement about the modern construction sequence rather than about the underlying grid, where no thirteen circles are privileged over any others.