Here is one way to do it.
Put your message in a large array.
Every 100mS, read out 32 bytes of the array and send it to the MAX7219.
Say 0 to 15 to start.
On the next 100mS, you move over 1 address in the array, and 1-16.
Then 2-17,
3-18,
4-19,
5-20,
and so on.
The array size is just limiteb by available SRAM.
Or, you can store it in PROGMEM for a larger array.
Or, you can store it in EEPROM, make your sketch fancier to allow changing it based on serial message received.
Lots of options.
