After our Dipankara Buddha was born, the entire world was lightened up, shining upon the beings in darkness. Thus, He was venerated as "Dipankara Buddha." This Buddha had the stability and would not be interfered by evils, demons, ghosts, or beings from other paths. His light illuminates every being's heart. "Heart" is very important.
The Tibetan king invited Master Padmasambhava to Tibet; Master Padmasambhava spent his whole life there spreading the Dharma of Mahavairocana Buddha, his Nine Vehicle Great Perfection Dharma. Because of Master Padmasambhava's power, it became a sacrad Buddhist place, and the school is called Tibetan Buddhism.
Compassion means love; He loves sentient beings, having unlimited, immense love for them. When one makes a request, He always responds to it, even though being always responsive is not His Vow... In many lifetimes, time and time again, He always becomes an icon of the saha world, the beloved one of sentient beings.
When Medicine Buddha is becoming a Buddha, first it requires a foundation. What is the foundation? Since millions of kalpas, His has a heart already - a heart of compassion. A person with a heart of compassion can perform deed of compassion...
Dizang Bodhisattva made a great vow before Sakyamuni Buddha entered nirvana: "Only after all beings are delivered shall I attain Bodhi; as long as all hells are not yet empty, I shall not achieve Buddhahood." His great vow has shaken the entire saha world.
Ksitigabha Bodhisattva's great vow did not come without a reason. He has been well known for delivering sentient beings in countless lives.
Sakyamuni Buddha from the East, Jesus from the West. The birth of a saint must have gone through hardships and difficulties. Without experiencing hardships, a saint cannot become a saint, can't attain Achievement, or even he becomes a saint, he will be persecuted by devils or demons...