This is the 9001st most frequent Japanese word.
注ぐ
To pour or flow (liquid); to concentrate or devote (effort, energy).
Here, 注ぐ is used in its primary meaning: to pour liquid into a stream or along a flow.
私は川の流れに沿って水を注いだ。
I poured water along the river flow.
In this sentence, 注ぐ metaphorically describes the action of sunlight flooding or pouring into a space.
朝日が窓からその部屋に光を注いでいた。
The morning sun poured light into the room through the window.
注ぐ in this context metaphorically refers to devoting effort, passion, or energy to an activity.