I was reading up on Emptiness, Samsara and so on and found out that
there is no individual soul or energy that reincarnates. Rather, it is
like a candle lighting another whereby the wax of the new candle is
different and has nothing in common with the previous candle.
Your question is about the Buddha but the Buddha never taught the above. The Buddha taught:
Bhikkhu, just as an oil-lamp burns in dependence on oil and a wick, and when the oil and wick are used up, if it does not get any more fuel, it is extinguished from lack of fuel; so too when he feels a feeling terminating with the body…a feeling terminating with life, he understands: ‘I feel a feeling terminating with life.’ He understands: ‘On the dissolution of the body, with the ending of life, all that is felt, not being delighted in, will become cool right here.’
MN 140
What you have read about a candle flame are later-day superstitions.
And I see that this image does not contradict (if there is no soul how
can there be rebirth?) the theme of rebirth when looked at it this
way.
But it does contradict. A flame cannot exist with a body of wax therefore when the wax is gone, just as when the body is lifeless, no flame can exist independent of a body of wax for the flame passes onto another candle. The candle flame analogy makes no logical sense at all.
If there is no individual, eternal essence (like the Atman in
Hinduism) that is liberated wouldn't that mean that life would go
extinct at a certain point?
The Buddha taught "liberation" is the absence of the mental states of greed, hatred & delusion, which includes giving "birth" to the idea of "self". "Samsara" and its ending is explained as follows:
"Just as a dog, tied by a leash to a post or stake, keeps running
around and circling around that very post or stake; in the same way,
an uninstructed, run-of-the-mill person — who has no regard for noble
ones, is not well-versed or disciplined in their Dhamma; who has no
regard for people of integrity, is not well-versed or disciplined in
their Dhamma — assumes form to be the self, or the self as possessing
form, or form as in the self, or the self as in form.
"He assumes feeling to be the self...
"He assumes perception to be the self...
"He assumes (mental) fabrications to be the self...
"He assumes consciousness to be the self, or the self as possessing
consciousness, or consciousness as in the self, or the self as in
consciousness.
"He keeps running around and circling around that very form... that
very feeling... that very perception... those very fabrications...
that very consciousness. He is not set loose from form, not set loose
from feeling... from perception... from fabrications... not set loose
from consciousness. He is not set loose from birth, aging, & death;
from sorrows, lamentations, pains, distresses, & despairs. He is not
set loose, I tell you, from suffering & stress.
"But a well-instructed, disciple of the noble ones — who has regard
for noble ones, is well-versed & disciplined in their Dhamma; who has
regard for people of integrity, is well-versed & disciplined in their
Dhamma — doesn't assume form to be the self, or the self as possessing
form, or form as in the self, or the self as in form.
"He doesn't assume feeling to be the self...
"He doesn't assume perception to be the self...
"He doesn't assume fabrications to be the self...
"He doesn't assume consciousness to be the self, or the self as
possessing consciousness, or consciousness as in the self, or the self
as in consciousness.
"He doesn't run around or circle around that very form... that very
feeling... that very perception... those very fabrications... that
very consciousness. He is set loose from form, set loose from
feeling... from perception... from fabrications... set loose from
consciousness. He is set loose from birth, aging, & death; from
sorrows, lamentations, pains, distresses, & despairs. He is set loose,
I tell you, from suffering & stress.
SN 22.99
I mean if I understand the Buddha correctly we all return to the one
"collective", true essence that he called the unborn, unchanging
etc... Doesn't that mean that at the point where all beings were
liberated life would cease to exist?
No. The word "unborn" means to not conceive thoughts of "self", as follows:
Bhikkhu, ‘I am’ is a conceiving; ‘I am this’ is a conceiving; ‘I shall
be’ is a conceiving; ‘I shall not be’ is a conceiving; ‘I shall be
possessed of form’ is a conceiving; ‘I shall be formless’ is a
conceiving; ‘I shall be percipient’ is a conceiving; ‘I shall be
non-percipient’ is a conceiving; ‘I shall be
neither-percipient-nor-non-percipient’ is a conceiving. Conceiving is
a disease, conceiving is a tumour, conceiving is a dart. By overcoming
all conceivings, bhikkhu, one is called a sage at peace. And the sage
at peace is not born, does not age, does not die; he is not shaken and
does not yearn. For there is nothing present in him by which he might
be born. Not being born, how could he age? Not ageing, how could he
die? Not dying, how could he be shaken? Not being shaken, why should
he yearn?
MN 140
So my question is why did he teach to free oneself from rebirth when
looked at it from the perspective I tried to describe?
The Buddha never taught to free oneself from "rebirth". There is no word spoken by the Buddha that means "rebirth". The Buddha taught to free the mind from "birth". "Birth" means to conceive & produce ideas of "self" and "beings", as follows:
"And what is birth? Whatever birth, taking birth, descent,
coming-to-be, coming-forth, appearance of aggregates, & acquisition of
[sense] media of the various beings in this or that group of beings,
that is called birth.
SN 12.2
Come to think of it the Buddha seemingly never answered questions of
the origins or the fundamental workings of the universe.
The Buddha said he only taught about suffering & the cessation of suffering (Alagaddūpama Sutta).
For example I know he was once asked what would happen to a fully
enlightened Buddha after death. To my knowledge he would answer
questions like this saying that it was meaningless to ask such things.
"Death" does not occur to a Buddha because a Buddha does not have the idea "I will die".
Did the Buddha know something about the non-self or the universe that
he purposefully never taught? Is the goal of a sentient being to join
the "one soul/ground of being" that is the unborn? But why? Is it
bliss to cease to exist and join a "homogenous mass of energy"?
The Buddha never spoke the above, which sounds like Hinduism.
Why is it important to sever the karmic cycle if it is obvious that
this is the way in which the universe manifests itself? In my opinion
the universe manifesting as this myriad life forms is a joyous loving
act and the whole point of the cosmic energy. I'm confused since I
read that part about the Buddha's teachings...
The Buddha taught the end of suffering. Ideas of "self" and "my kamma" causes suffering.