This meeting is different from the others.
There had been four in total, spread out over five months. The Order members were all young; five months ago they had been fresh out of school and full of ideas and dreams and morals. They had been new to war and death and loss; they hadn't been able to comprehend that life wasn't forever.
Back then they hadn't known just how innocent and naïve they really were.
Dumbledore's speech comes to a melancholy end.
"United we stand; divided we fall."
Yes, things have changed, if suddenly Albus Dumbledore is grave and warning.