This says that if you have a choice of bids and one of the options is 3NT, bid 3NT. The idea is that 3NT requires the fewest tricks for game and, even if there is a winning defence, the defenders may get off to the wrong lead.
The options here are 3NT, 4♣ and double. Although you do not have a certain spade stopper, you need far less help from partner to make 3NT than 5♣ or 4♥. In any case, North is most unlikely to lead the ♠A. Bid 3NT.
