Genesis 18:13

13.And the Lord said. Because the majesty of God had now been manifested in the angels, Moses expressly mentions his Name. We have before declared, in what sense the name of God is transferred to the angel; it is not, therefore, now necessary to repeat it: except, as it is always important to remark, that the word of the Lord is so precious to himself, that he would be regarded by us as present, whenever he speaks through his ministers. Again, whenever he manifested himself to the fathers, Christ was the Mediator between him and them; who not only personates God in proclaiming his word, but is also truly and essentially God. And because the laughter of Sarah had not been detected by the eye of man, therefore Moses expressly declares that she was reprehended by God. And to this point belong the following circumstances, that the angel had his back turned to the tent, and that Sarah laughed within herself, and not before others. The censure also shows that the laughter of Sarah was joined with incredulity. For there is no little weight in this sentence, ‘Can anything be wonderful with God?’ But the angel chides Sarah, because she limited the power of God within the bounds of her own sense. An antithesis is therefore implied between the immense power of God, and the contracted measure which Sarah imagined to herself, through her carnal reason. Some translate the word פלא (pala,) hidden, as if the angel meant that nothing was hidden from God: but the sense is different; namely, that the power of God ought not to be estimated by human reason. (414) It is not surprising, that in arduous affairs we fail, or that we succumb to difficulties: but God’s way is far otherwise, for he looks down with contempt, from above, upon those things which alarm us by their lofty elevation. We now see what was the sin of Sarah; namely, that she did wrong to God, by not acknowledging the greatness of his power. And truly, we also attempt to rob God of his power, whenever we distrust his word. At the first sight, Paul seems to give cold praise to the faith of Abraham, in saying, that he did not consider his body, now dead, but gave glory to God, because he was persuaded that he could fulfill what he had promised. (Romans 4:19.) But if we thoroughly investigate the source of distrust, we shall find that the reason why we doubt of God’s promises is, because we sinfully detract from his power. For as soon as any extraordinary difficulty occurs, then, whatever God has promised, seems to us fabulous; yea, the moment he speaks, the perverse thought insinuates itself, How will he fulfill what he promises? Being bound down, and preoccupied by such narrow thoughts, we exclude his power, the knowledge of which is better to us than a thousand worlds. In short, he who does not expect more from God than he is able to comprehend in the scanty measure of his own reason, does him grievous wrong. Meanwhile, the word of the Lord ought to be inseparably joined with his power; for nothing is more preposterous, than to inquire what God can do, to the setting aside of his declared will. In this way the Papists plunge themselves into a profound labyrinth, when they dispute concerning the absolute power of God. Therefore, unless we are willing to be involved in absurd dotings, it is necessary that the word should precede us like a lamp; so that his power and his will may be conjoined by an inseparable bond. This rule the Apostle prescribes to us, when he says,

‘Being certainly persuaded, that what he has promised,
he is able to perform,’ (Romans 4:21.)

The angel again repeats the promise that he would come ‘according to the time of life,’ that is, in the revolving of the year, when the full time of bringing forth should have arrived.