Why did Tathagata seal the Tang Priest?

Tang Priest was named Tathagata's merit Buddha. It refers to a Buddha with a very noble character, but it is actually praising the quality of Tang Priest. This is also an affirmation of Tang Priest's experience in the "81 Difficulties" and his experience in "Don't forget your initiative". In addition, the Tang Priest, also known as Tang Sanzang, was born in Luoyang, Henan Province, based on Xuanzang, a monk in the Tang Dynasty, with a common name of "Chen Yi".