The exhibition space at Axel’s Frame Shop & Gallery is modest — just one wall opposite the framing area and displays devoted to local artisans. But a trip to the Waterbury venue will reward visitors, with or without framing needs, with compelling visual statements from four featured artists. Kate Longmaid, Ann Young, Jerry Ralya and Michelle Saffran pack a lot into that small space, responding to the theme of social injustice — racism, sexism, genocide and religious persecution — with evocative paintings, pastel drawings and photography. The works are as timely as they are cogent.