Butterflies undergo marvellous metamorphoses during their life cycles and this phenomenon caught the attention of the ancient peoples:

A butterfly is an insect of the order Lepidoptera. Like all Lepidoptera, butterflies are notable for their unusual life cycle with a larval caterpillar stage, an inactive pupal stage, and a spectacular metamorphosis into a familiar and colourful winged adult form ...

According to the 'Butterflies' chapter in Kwaidan: Stories and Studies of Strange Things, by Lafcadio Hearn, a butterfly is seen as the personification of a person's soul; whether they be living, dying, or already dead ... The Ancient Greek word for 'butterfly' is ψύχη (psychē), which primarily means 'soul', 'mind' ...

The Taoist philosopher Zhuangzi once had a dream of being a butterfly flying without care about humanity, however when he woke up and realized it was just a dream, he thought to himself 'Was I before a man who dreamt about being a butterfly, or am I now a butterfly who dreams about being a man?' In some old cultures, butterflies also symbolize rebirth into a new life after being inside a cocoon for a period of time ...

(Wikipedia)

The butterfly has 4 life stages: egg, caterpillar, pupa, and imago. The beautiful last stage - symbolizing the 'soul' or 'spirit' - arrives after a period of stillness (pupa). The egg stage is also a period of stillness, while on the other hand the voracious caterpillar eats and eats in order to grow.

The 4 life stages of the butterfly were chosen to illustrate how during the yearly cycle of the sun (also yellow as butter) the beginning comes at winter solstice (egg) and how at the midstation (summer solstice, pupa) another season of rest arrives.

When 'in some old cultures' rebirth was likened to the emergence from a pupa, the pupa - presumably -in turn was likened to the egg. Birth originates from an egg, rebirth from a pupa.

Spring is like the caterpillar, a season of growth, while autumn is the opposite, a season of decline. Spring is a season of life, autumn a season of death. According to English Etymology:

pupa ... chrysalis ... modL. use by Linnæus (1758) of L. pūpa, doll; cfr PUPPET.

puppet ... †doll; (human) figure jointed and moving on strings or wires ... lathe-head ...

chrysalis ... form taken by an insect in the stage between larva and imago ... L. chrysal(l)is ... Gr. khrūsallis gold-coloured sheath of butterflies, f. khrūsós gold ...

imago ... (entom.) final stage of an insect ... Mod. use (by Linnæus, 1767) of L. imāgō IMAGE.

image ... artificial representation of an object, likeness, statue; (optical) counterpart ... mental representation ... rel. to IMITATE ...

The imago stage is just an imitation of the spring stage. Ghosts are just mirages. The stone statues on Easter Island are not real persons, only representations of them.

Why is it forbidden in some cultures to make images of the god(s)? Answer: Because that would threaten to kill them.