What is jim worried about when Mr. Shimerda Kneels before the Burdens Christmas tree

I'm not sure what Jim worried about but this is the paragraph:

As it grew dark, I asked whether I might light the Christmas tree before the lamp was brought. When the candle-ends sent up their conical yellow flames, all the coloured figures from Austria stood out clear and full of meaning against the green boughs. Mr. Shimerda rose, crossed himself, and quietly knelt down before the tree, his head sunk forward. His long body formed a letter ‘S.’ I saw grandmother look apprehensively at grandfather. He was rather narrow in religious matters, and sometimes spoke out and hurt people’s feelings. There had been nothing strange about the tree before, but now, with some one kneeling before it—images, candles... Grandfather merely put his finger-tips to his brow and bowed his venerable head, thus Protestantizing the atmosphere.