The Sun lit, from dark and quiet matter, into the steady burn that has been going on for millennia, because of a series of events. This series of events has taken place elsewhere, and often. It is the standard solar system panoply, in fact. The steps are as follows. First, matter and energy are homogenized by a big bang process, which is only setting the clock back to zero or wiping the slate clean, so to speak. The process, for this portion of the Universe, is reset. Coming out of this big bang situation matter and energy begin to congeal, into all the many sub-atomic particles that form not only what humans understand to be matter and energy, but many more such particles, including the particles that make up the soul. During this congealing period there is little interaction. It is as though there is not enough of anything to get into a contest. Small fry don't squabble.
Gradually the congealing process produces planets that orbit each other. This happens as matter has a natural attraction and repulsion for and against other matter, and as the congealing process takes place attractions start movement but repulsion causes a circular dance. Imagine a dance where all the potential partners are undecided. They approach and then circle. Everything gets into motion.
At this point all is dark, the form and the void that the Bible refers to. So what starts the light? Continued congealing, which in time produces pressure that starts yet another process. This process converts matter into energy, which is what is occurring within the Sun. Humans make assumptions about the composition of suns, assuming light elements such as helium, and about the burning process, assuming fusion with radioactive byproducts. They are incorrect on both counts. A mass as large as a sun does not light, due to compression, unless key elements in the heavy element spectrum are present to a sufficient degree. There are dead suns, smoldering suns, and lit suns, and the dye is cast in this matter when the suns are first formed. Humans assume the burning process to be radioactive because their only experience with intense production of heat and light also produces intense radioactivity. Should this be the case, would not life on Earth be suffering from radiation poisoning?
Such volumes of energy emerge from such tiny amounts of what humans term matter, that the seemingly violent brilliance of the Sun comes from very little mass. Of course, the Sun is diminished as this goes on, but by such a tiny amount. In the scheme of things, not to matter at all. Over time, the pressure within the Sun takes two simultaneous courses. One, the mass of the Sun shrinks to where the burning or conversion action slows down. The pressure has diminished, due to the reduced mass. As the Sun cools, its matter shrinks and compresses, a natural process known to humans. Cold things are more dense than hot things. This eventually sets off the second reaction of a dying star, the super nova or explosion. The Sun lights again, for one last time, this time in a violent and uncontrolled burn that sends its remaining particles off every which way.