Halakhah su II Re 23:37

It is customary that all those attending a circumcision, stand throughout the ceremony, for it is said, "And all the people stood in the covenant,"³II Kings 23:3. excepting the sandek, who holds the baby while seated. After the father recites the berachah, Lehachniso, and those assembled answer amein, they all say, "Just as he was initiated into the covenant, so may he be initiated into the study of Torah, to the Chupah, and to the performance of good deeds."