I find it interesting that despite Arnold BĂścklin creating "Isle of Life" as a counterpart to "Isle of The Dead", only the latter painting (rather, one of its versions) is most known and popular. I can't tell exactly why that is but i can speculate a little.
Sure, the answer may be "the eternal human morbid curiosity with all things dark and scary" but notice how this painting does not have any obvious displays of death and suffering at all. Even without knowing the name of the image, it leaves an uneasy feeling: this is no coincidence, because the painting was not originally meant to have any connection to death or mourning. The little detail of an oarsman, rowing a tiny boat with a mysterious white figure standing in front of what appears to be a coffin, decorated in flowers, similar to reliefs found on ancient Roman coffins, was added much later, by request of his visitor, a widow who asked BĂścklin to add an homage to her deceased husband to the painting. Subsequently, the painter liked the idea so much, he added it to every other, even earlier, already finished, version.
It's unsurprising, considering how it draws immediate attention of the viewer, being the only sign of human life and source of movement in the painting.
"Isle of The Dead" was originally meant to only produce the sense of stillness, with it's strict composition, thin, straight cypresses and cliffs almost devoid of vegetation. The architectural elements and completely still waters emphasise this feeling.
However, a little boat breaks this dreamy stiffness, giving the isle itself a purpose. Now it's not a desolate, forgotten land, but a destination. We don't see where the figures are headed - the centre of the island is heavily obscured by the shadow and the cypresses - trees known for their still, almost geometrically perfect shape and dark foliage. Cypresses are commonly associated with Mediterranean coast, and ancient Greek legends give this tree a tragic backstory, making it a symbol of mourning and grief (keep in mind that BĂścklin was mainly known for illustrating Greco-Roman legends so people familiar with his work would immediately start looking for connections to existing myths). Combined with the boat, floating across waters, this results in many viewers interpreting the island as an entrance to the underworld, with oarsman being Charon, crossing the river Styx to bring the souls of the dead to the world of dead. We don't see any indication of the painting being set in real or mythological world, save for subtle references to ancient Greece or Rome, we can't tell anything about the identity oarsman or the passenger. Is the white figure a mourning family member or a friend, or are themselves dead and carrying their own coffin?
In the centre of the isle there may just be a graveyard, a mausoleum or a tomb - in fact, the first German name for the painting was "The Tomb Island". But then, why is it on such a tiny island in the middle of a body of water with no sign of big land? Why are there entrances carved into stone of the cliffs, guarding the isle from almost all sides save for a small entrance in the front? There must be, or had been a purpose to them. Are they important to some kind of ritual? Does anyone live there? How? There are no stairways so a normal human can't climb up there easily. Are those abandoned ruins that were used for something unrelated to the current purpose of the island? There's no answer.
The setting sun, obscured from the sight of the viewer, is also associated with old age and dying by many cultures - in fact, the most of other versions of this painting are set during the dead of night, the time of darkness, rest and simultaneously fear. Gathering clouds, indicating the incoming storm, blend the skies and water, the border between the material and divine.
The coffin and the boat are the only items with a clear purpose in the image, but they only hint at the meaning of the image, of the process happening within the world, displayed on the painting, but don't give clear answers. We have a starting point - two people carrying a coffin, but we don't have an ending point to arrive to: who knows who they are or what they're going to do? Where exactly are they going?
This intrigue and mystery is obviously absent in the 'Isle of Life'
It's still serene, but more lush and dynamic. The connection to ancient Greek/Roman culture or at least romanticised view of it in European art here is a bit more apparent with flowing robes and veils, flower crowns. This island is a bit bigger - maybe it's even very large, but long - we can't tell from this angle, so the land on it allows for a bit of freedom of movement, in fact, we see a crowd celebrating something in the middle of an isle.
We don't see any boats so we can't tell how people got there, if they're stuck or if there's a big land they came from that we can't see. People walking in water around the island shows how shallow and safe the waters are. Maybe it's an island near the shore, that can be reached by foot? The tree cut off on the left of the painting also breaks the composition, implying there's something that we can't see happening outside of the bounds of the painting. It surely is a very idealised portrayal of nature - some kind of Elysium - swans swim near people without fearing them, people interact with each other and nature with curiosity and friendly intentions. The flora is very diverse: multiple different types of trees grow near each other in a way that's usually not very realistic for wildness and more commonly found in maintained gardens. Even the waters are shallow and safe enough to walk in. The weather is warm and sunny, the horizon also blends with the skies, the whole image is aimed at producing the sensation of calm and maybe yearning, but it doesn't leave much place to wonder and meditate upon.
What are these people doing? I don't know, but they seem to be having fun. Where are they? Who knows, but they're clearly safe. A process is happening - people are swimming, talking, gathering, but there's no end goal to worry about. With all of its dynamic movement, 'Isle of Life' is more still than 'Isle of The Dead'. While the boat with a strange coffin with clearly swim ashore, the crowd can celebrate for eternity with no end or purpose.
That's not to say that all depictions or paradise or dreamy, peaceful places are boring. BĂścklin himself has plenty of such paintings, but he's the best at depicting stillness and quiet peace, not vivacity and motion, especially in light-hearted settings.
