Numbers 14:17

17.And now, I beseech thee, let the power of my Lord be great. He derives another ground of confidence from the vision, in which God had more clearly manifested His nature, from whence it appears how much he had profited by it, and what earnest and anxious attention he had paid to it. Hence, however, we derive a general piece of instruction, that there is nothing more efficacious in our prayers than to set His own word before God, and then to found our supplications upon His promises, as if He dictated to us out of His own mouth what we were to ask. Since, then, God had manifested Himself to Moses in that memorable declaration, which we have already considered, he was able to derive from thence a sure directory for prayer; for nothing can be more sure than His own word, on which if our prayers are based, there is no reason to fear that they will be ineffectual, or that their results should disappoint us, since He who has spoken will prove Himself to be true. And, in fact, this is the reason why He speaks, viz., to afford us the grounds for addressing Him, for else we must needs be dumb.