The Balance is at the centre of the universe/multiverse. In its simplest form it shows how far the cosmos is out of balance as it tips to either Law or Chaos. At its centre the Balance pivots on Time itself.
When the universe is formed it is in perfect balance. If the balance tips to either absolute Law or total Chaos then time comes to an end. If a multiverse is formed then a conjunction of all the dimensions will also lead to the end of time.
When time ends, a new universe is formed. A multiverse is not certain. Paradoxical events, like the Sundering, are necessary to create a multiverse. The dimension at the centre of the multiverse is FirstWorld, the original universe. It is not known whether the multiverse is infinite and this is a major bone of contention between scholars. There is an argument that an infinite universe could never tip fully to Law or Chaos and so in an infinite multiverse time could never end.
The Balance is, by all human definitions, God. Only it and four icons can pass from the end of time in one universe/multiverse to the next. One of those icons is Time in its physical incarnation the Guardian of Tomorrow.
Absolute Law is stagnation with all change prevented by rigid rules.
Total Chaos is anarchy without any rules at all.
Neither side has a monopoly on good or evil. There are degrees of goodness and evilness in everybody. Pure goodness or total evil are very rare.