Now as one who teaches to swim, at first indeed placing his hands under his pupils, carefully supports them, but afterward frequently withdrawing his hand, bids them help themselves, nay even lets them sink a little; so likewise did Christ deal with His disciples. At the beginning truly He was present to them, giving them most richly abundance of all things; as it follows, And they said unto them, Nothing. But when it was necessary for them to shew their own strength, He withdrew from them for a little His grace, bidding them do something of themselves; as it follows, But now he that hath a purse, that is, wherein to carry money, let him take it, and likewise his scrip, that is, to carry provisions in. And truly when they had neither shoes, nor girdle, nor staff, nor money, they never suffered the want of any thing. But when He allowed them purse and scrip, they seem to suffer hunger, and thirst, and nakedness. As if He said to them, Hitherto all things have been most richly supplied to you, but now I would have you also experience poverty, therefore I hold you no longer to the former rule, but I command you to get purse and scrip. Now God might even to the end have kept them in plenty, but for many reasons He was unwilling to do so. First that they might impute nothing to themselves, but acknowledge that every thing flowed from God; secondly, that they might learn moderation; thirdly, that they might not think too highly of themselves. For this cause while He permitted them to fall into many unlooked for evils, He relaxed the rigour of the former law, lest it should become grievous and intolerable.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).
Also cites: in illud ad Rom. 16. Salutate Priscillam.