Heaven-Defying Taoist was training soldiers and imparting Taoist magic to boost the cultivation levels of these guards at the drill ground.
Within Qingyang Temple, Yuan Tiangang was crafting elixir pills to enhance cultivation levels. Utilizing elixir pills for this purpose was greatly taboo, as even after the enhancement, one needed to meditate and comprehend their realm to avoid obstructing their future path. However, it was different for these guards. They were directly elevated to the ninth realm of Immortals using a large number of elixir pills and taught the Seventy-Two Transformations of Earthly Fiends before being sent to the front lines.
The inclusion of these guards indeed significantly boosted the military strength of the Tang army, since soldiers at the ninth realm of Immortals were rare.