@Anonymous
A block is a collection of AutoCAD objects nested together and given a name (Chair, Tree, etc.). As a block you can copy and move them easier than if they were separate objects (lines, arcs, etc). Another benefit is that if you edit one - then ALL copies in your drawing update.
If the objects that go into a block are created on Layer 0 then the block and all of it's individual objects (lines, arcs, etc) go on the layer you select. Layer 0 is our "Transparent" layer.
If the objects that go into the block are created on any layer OTHER than 0 (Layer CHAIR for example) then those objects STAY on that layer, even if you put the block on a different layer (Layer FURNITURE for example). The BLOCK (parent) is on one layer (FURNITURE) while the objects making up the block (the lines, arcs, etc) are on layer CHAIR. This method forces the block objects to always take on the properties of the layer they were created on - while the parent block visibility can be controlled separately. Example - I can have the chairs take on the properties of the layer CHAIRS, the beds take on the properties of the layer BEDS, etc. and have them ALL belong on the layer FURNITURE. If I FREEZE the FURNITURE layer, they all go away. Otherwise I can control them each by their individual layers.