When can a deed be an act of woship?

Answer- If there are two things: perfect love (for Allah) along with perfect subjection (to Him).

Allah Almighty says:

{But those who believe, love Allah more (than anything else)}.

(Al-Baqarah, 165)

Allah the Almighty says

{Verily those who live in awe for fear of their Lord}.

(Al-Mu'minun , 57)

Allah the Almighty gathered the two things in the following verse that reads,

{Verily, they used to hasten on to do good deeds, and they used to call on Us with hope and fear, and used to humble themselves before Us}.

(Al-Anbiya', 90)