1. Warmth and fervency in prayer. To open the mouth is in effect to open the heart, that it may be both engaged and enlarged... We may be said to open our mouths wide when our affections are quick and lively, and there is a correspondence between the feelings of the heart and the request of the lips; or when we really pray, and not merely seem to do so. This is strongly and beautifully expressed in Ps 119:131: I opened my mouth, and panted: for I longed for thy commandments.
2. It implies a holy fluency and copiousness of expression, so as to order our cause before him, and fill our mouths with arguments. When the good man gets near to God, he has much business to transact with him, many complaints to make, and many blessings to implore; and, as such seasons do not frequently occur, he's the more careful to improve them. He then pours out his whole soul, and is at no loss for words; for when the heart is full, the tongue overflows. Sorrow and distress will even make those eloquent who are naturally slow of speech.
3. Enlarged hope and expectation. We may be too irreverent in our approaches to God, and too peremptory in our application; but if the matter and manner of our prayer be right, we cannot be too confident in our expectations from him... Open thy mouth wide then, O Christian; stretch out thy desires to the uttermost, grasp heaven and earth in thy boundless wishes, and believe there is enough in God to afford the full satisfaction. Not only come, but come with boldness to the throne of grace: it is erected for sinners, even the chief of sinners. Come to it then, and wait at it, till you obtain mercy and find grace to help in time of need. Those who expect most from God are likely to receive the most. The desire of the righteous, let it be ever so extensive, shall be granted.
1. If we open our mouths to God in prayer, he will fill them more and more with suitable petitions and arguments. When we attempt to open the mouth, God will open it still wider. Thus he dealt with Abraham when he interceded for Sodom; the longer he prayed, the more submissive and yet the more importunate he became. By praying we increase our ability to pray, and find a greater facility in the duty. "To him that hath shall be given, and he shall have more abundantly."
2. God will fill the mouth with abundant thanksgivings. Many of David's psalms begin with prayer, and end with the most animated praises. No mercies so dispose to thankfulness as those which are received in answer to prayer; for according to the degree of desire will be the sweetness of fruition ...
3. We shall be filled with those blessings we pray for, if they are calculated to promote our real good and the glory of God. Do we desire fresh communications of grace, and manifestations of divine love; a renewed sense of pardoning mercy, and an application of the blood of Christ? Do we want holiness, peace, and assurance? Do we want to hear from God, to see him, and be like him? The promise is, My God shall supply all your need according to his riches in glory by Christ Jesus, Php 4:19. You shall have what you desire, and be satisfied: it shall be enough, and you shall think it so. "The Lord will give grace and glory: no good thing will he withhold from them that walk uprightly."