The postcard shows another oil painting by Vicente Manansala entitled Prayer Before Meals. I couldn't find additional information about the painting nor its location (private collection or museum).
Grace is a name for any of a number of short prayers said or an unvoiced intention held prior to partaking of a meal. A prayer of Grace is said to be an act of offering thanks to God for granting humans dominion over the earth and the right and ability to sacrifice the lives of divine creations for sustenance; this thanks is the "saying of Grace" prior to and/or after eating of any meal.
Grace Wikipedia Entry