Ray and zphenyl, thank you!
Center stand is great for changing oil. But, if I were to check the oil level with center stand, it shows that there is no oil. For an accurate reading, I would need to take it off the center stand to make sure both wheels are touching the ground and also make sure the bike is perfectly upright.
When the bike is on the center stand, both wheels are not at the same level. The front wheel is touching the ground, and the rear wheel is off the ground.
The idea behind the jack is to raise the bike so that everything is at the same level. This is just to avoid the extra step of taking the bike off the center stand and checking the oil level.
I might have to try what Jfro5867 recommended.