Charles H. Spurgeon on Psalms 119:131

I opened my mouth, and panted. By this manner of speech, David expresses, as Basil thinks, animi propensionem, that the inclination of his soul was after God's word. For, this opened mouth, Ambrose thinks, is os interioris hominis, the mouth of the inward man, which in effect is his heart; and the, speech notes vehementem animi intensionem, a vehement intension of his spirit, saith Euthymius. Yet shall it not be amiss to consider here how the mind of the godly earnestly affected moves the body also. The speech may be drawn from travellers, who being very desirous to attain to their proposed ends, enforce their strength thereunto; and finding a weakness in their body to answer their will, they pant and open their mouth, seeking refreshment from the air to renew their strength: or as Vatablus thinks, from men exceeding hungry and thirsty, who open their mouth as if they would draw in the whole air, and then pant and sigh within themselves when they find no full refreshment by it. So he expresses it: "My heart burns with so ardent a longing for thy commandments, that I am forced ever and anon to gasp by reason of my painful breathing."

However it be, it lets us see how the hearing, reading, or meditating of God's word wakened in David a most earnest affection to have the light, joy, grace, and comfort thereof communicated to his own heart. For in the godly, knowledge of good increaseth desires; and it cannot be expressed how vehemently their souls long to feel that power and comfort which they know is in the word; and how sore they are grieved and troubled when they find it not.

And happy were we, if we could meet the Lord with this like affection; that when he opens his mouth, we could also open our heart to hear, as David here doth. Christus aperit os, ut daret allis spiritum; David aperuil ut acciperet;offering his heart to receive the spirit of grace, when God openeth his mouth in his word to give it. For it is his promise to us all "Open thy mouth wide, and I will fill it." Let us turn it into a prayer, that the Lord, who opened the heart of Lydia, would open our heart to receive grace when he offers by his word to give it. William Cowper.