을 열고

… open and

→ 을

phrase Very common #1,148

… open and 을 marks the preceding noun as the object of 열다 (“to open”). With 마음 (“heart/mind”), 마음을 열고 often means “with an open heart” or “openly.”

KO: 문을 열고 들어오세요.

EN: Open the door and come in.