strong point
A subject, activity, or field at which one is particularly skilled or adept, or one's foremost virtue. Working with computers has never been my strong point, so this position is going to be a real challenge for me. Patience is Sam's strong point. I've never seen him lose his temper.
strong point
Also, strong suit. An area in which someone or something excels, as in That beautiful lobby is the building's strong point, or Writing is her strong suit. The first term was first recorded in 1840; the variant alludes to various card games, in which it signifies the suit with the highest or most cards.