If God promises something, then faith must fight a long and bitter fight, for reason or the flesh judges that God's promises are impossible. Therefore faith must battle against reason and its doubts. The Devil, too, approaches us with promises, and indeed such as seem very plausible. It certainly requires at times a keen mind rightly to distinguish between God's true and the Devil's false promises. The promises of the Devil are seemingly very pleasant and acceptable. Faith is something that is busy, powerful and creative, though properly speaking, it is essentially an enduring than a doing. It changes the mind and heart. While reason holds to what is present, faith apprehends the things that are not seen. Contrary to reason, faith regards the invisible things as already materialized. This explains why faith, unlike hearing is not found in many, for only few believe, while the great majority cling to the things that are present and can be felt and handled rather than to the Word.
This, then, is the mark of the true divine promises, that they are contrary to reason so that it refuses to believe them. The promises of the Devil, on the contrary, are in full agreement with reason and are readily and uncritically accepted. God's promises which are true and faithful, lead to the cross, and by the cross to His eternal blessing. Therefore reason is offended at them in two ways. It regards as nothing what is invisible and far away in the future, and it detests the cross as a calamity that is everlasting and without end. That is the reason why despite the riches of the divine promises, few believe them. These are such whose hearts are led by the Holy Spirit so that, as Abraham, they defy all foes and cling to the Word of God who calls them.
Before Abraham came to Canaan he was blessed in many ways, but in the land of promise, he, despite his strong faith was forced to go into another country to escape the fury of the famine. God does this purposely to try the faith of His saints. However after a short time, He restores to them not only earthly prosperity, as Abraham became very wealthy, but He also gives them a greater faith and a deeper experience of His divine grace and mercy. For this reason Paul says in Romans 5:3 that though God's saints sigh under their cross, yet they glory in their tribulations when they discover how wonderfully God directs their life.
God thus proves Himself the Protector of all that put their trust in Him. He tries their faith by chastisements, but never forsakes them. Finally, He gloriously delivers them and at the same time benefits others with them.