Add this to the end of setup()
// copy the text to display buffer
for(int u = 0; u < 3; u++)
display_buffer[u] = text_to_display.charAt(u);
// send the buffer to the display
for(int i = 0; i < 4; i++)
disp.writeDigitAscii(i, display_buffer[i]);
// // display the text
disp.writeDisplay();
and clear all from the loop()