The connection between Frodo and Sam recalls the spiral form. Frodo’s hand spirals around Sam’s, firmly taking him by the wrist.
Image rendered to emphasis the ‘spiral link’ between Frodo and Sam.
Spirals have been seen throughout Fellowship for example:
The crown spiral of Galadriel.
Spirals have signified a mystical union and hidden power.
Annunciating light The light that falls on the surface is an annunciating light. This light will forge a mystical union between Frodo and Sam. Frodo and Sam will become a trinity. Master, servant and mystical light. This trinity will walk into Mordor.
See also how the light is a benign presence. It radiates out like a divine, benign version of the Eye of Sauron.
Frodo is alone. His decision is to go on alone. The tears that flow are not from weakness. Tears come when Frodo is learning an inner lesson and will carry it into action. Frodo has come a long way. Frodo’s face here is full of experience. Frodo is now an experienced hero. Compare this to the puckish innocence when he is about to leave the shire.
Sam is motivated by faith. Sam pushes through the water. See how the wake of the hobbit makes him look like an arrow. The target is Frodo. Sam wants to be with the object of his devotion.