The limits of civil obedience are clearly drawn. It is a duty, because 'the powers that be are ordained of God,' and obedience to them is obedience to Him. But if they, transcending their sphere, claim obedience which can only be rendered by disobedience to Him who has appointed them, then they are no longer His ministers, and the duty of allegiance falls away. But there must be a plain conflict of commands, and we must take care lest we substitute whims and fancies of our own for the injunctions of God. Peter was not guided by his own conceptions of duty, but by the distinct precept of his Master, which had bid him speak. It is not true that it is the cause which makes the martyr, but it is true that many good men have made themselves martyrs needlessly. This principle is too sharp a weapon to be causelessly drawn and brandished. Only an unmistakable opposition of commandments warrants its use; and then, he has little right to be called Christ's soldier who keeps the sword in the scabbard. The articulate refusal in verse 20 bases itself on the ground of irrepressible necessity: 'We cannot but speak.' The immediate application was to the facts of Christ's life, death, and glory. The Apostles could not help speaking of these, both because to do so was their commission, and because the knowledge of them and of their importance forbade silence. The truth implied is of wide reach. Whoever has a real, personal experience of Christ's saving power, and has heard and seen Him, will be irresistibly impelled to impart what he has received. Speech is a relief to a full heart. The word, concealed in the prophet's heart, burned there 'like fire in his bones, and he was weary of forbearing.' So it always is with deep conviction. If a man has never felt that he must speak of Christ, he is a very imperfect Christian. The glow of his own heart, the pity for men who know Him not, his Lord's command, all concur to compel speech. The full river cannot be dammed up.