Why did Augustine temper his external response in the presence of his friend

Augustine must come to terms with her death instead of riling against it. Augustine felt extraordinary pain at his mother's death but resolved not to grieve too greatly, for she had gone home to God. He cannot say why he was so saddened by her death, but threw himself on God's mercy, asking for comfort. He says that it is fitting to weep before God and rely on his infinite compassion.