The speaker is talking to someone struggling with depression and anxiety, and the poem builds its comfort around one extended metaphor: the mental illness is an ocean. The speaker stands on land and watches the other person go under, which is an honest, slightly uncomfortable picture. They can't swim in and rescue anyone; they can only watch and wait.
What keeps the poem hopeful is the idea that hitting the bottom isn't the end. The fall itself gives the push back upward. The speaker promises to be there when the person surfaces, ready to pull them up.
The last lines are the most interesting. The speaker says they stood there knowing the person could do it, not hoping they would drown. Watching in silence could look like indifference, and the speaker wants to correct that reading. "Your job is to find the difference" leaves the listener to see the faith behind the distance. The mood is steady, firm and caring, with a touch of tough love.