【Readiness】 , 【ease】 ,  【facility】 ,  【dexterity】  are comparable when they mean the power of doing something without evidence of effort, or the quality of work that manifests such effortlessness.

【Readiness】 lays stress on the quickness or promptitude with which something is done.

【Ease】 , which is probably more often used of the quality than of the power, suggests not only a lack of all signs of strain or care but an absence of signs of hesitation or uncertainty, with resulting evenness in performance and, especially in spoken or written discourse, fluency, directness, grace, and simplicity in expression.

【Facility】 is sometimes used in a derogatory sense nearly equivalent to shallowness.

More frequently this feeling is lost and  【facility】  may be interchangeable with  【ease】 , though it tends more often than  【ease】 to express the power, proceeding from practice and use, of performing an act or dispatching a task with lightness and address.

【Dexterity】 implies both 【readiness】 and 【facility】 , but it carries a stronger implication than any of the preceding words of previous training or practice and of proficiency or skill.