Square Enix's Final Fantasy 7 Remake is filled with small details that are easy to miss, and this includes Aerith's mural shown in Chapter 17. The colorful image has a lot of symbolism that hints at things she knows and the deeper story in general.
[Warning: Final Fantasy 7 Remake And Original Spoilers Below]
In Chapter 17 in Final Fantasy 7 Remake's Shinra building, Aerith and the gang end up in a room she describes as the one she grew up in as a child, and players can see a mural on the wall that she painted during that time. She explains she's a descendant of the Ancients, or Cetra, which prompts Barrett to recite a poem about returning to the Promised Land.
The Whispers appear, and Red XIII explains they're drawn to those who attempt to alter destiny, likening it to the Lifestream, or "the flow of the great river that is the planet, from inception to oblivion." A closer look at the mural on the wall depicts the cyclic Lifestream, among other details. At a glance, the mural shows an evolution of Aerith's drawings, starting from the very bottom's rudimentary childish sketches to the progression of skill and detail shown above, as she grew older and taller.
Final Fantasy 7 Remake: Hidden Details In Aerith's Mural
More than just a child's drawing, Aerith's mural shows the oblong, green Lifestream - which according to Red XIII's description - can also be thought of as both destiny and time flowing in a circular manner, and notable events that are supposed to happen or have already occurred can be seen as well. In the bottom left, the people shown are likely the Cetra, who would migrate around the planet, healing it each time they settled. Just above them are five more figures in robes - perhaps Cetra sages - that appear to be creating Materia, depicted as small colorful orbs above them.
The top left shows a pyramid-like building. This is likely the Temple of the Ancients, but the rounded structure on top is reminiscent of the Sector 5 church or even Bugenhagen's observatory as they were portrayed in the original FF7 game. Following the flow to the right, it appears the Lifestream takes the form of different beasts, likely a means for protecting itself. The green dragon creature could be the summon Bahamut, and the horned dragon/wolf figure could be another Summon or even a Weapon created by the planet. It somewhat resembles Ultimate Weapon from the original Final Fantasy 7, due to the horn. It appears these green beasts are battling a black, monstrous entity - perhaps a general representation of evil. A phoenix appears to the right of that, which is another symbol of cycles and also rebirth.
The flowers, land, and sea creatures that connect the Lifestream on the right seem to portray what all it and the planet encompass. In the middle, a big yellow flower is shown, which could represent the planet as a whole. The church flowers are often shown as a representation of the planet itself, which Aerith - a Cetra - tends and protects as is the Ancient's role to defend the planet. Around it, a white glowing orb is shown. This is likely Holy (the strongest White Magic spell) that is summoned from the White Materia that Aerith carries in her hair. It's protecting the flower (planet) from Meteor, which is seen falling to its top right, in the exact same direction as both the original and FF7 Remake's logo shows it falling. What looks like the sun is there too, confirming Meteor descending from space. What looks like the summon, Leviathan, can be seen - another weapon or means of protection from the planet.
The symbolism of cycles appears multiple times throughout Final Fantasy 7 Remake, from the beginning where Aerith opens her eyes (which is how the original ends) to the title screen and ending showing Cloud's sword lodged in the ground, and even the center of Aerith's mural being shaped similar to the cosmos at The Edge of Creation during the ending of the game (see TL;DR slides for reference). This idea of cyclic time could hint at Remake's occurrence in relation to the original game.