2♦ is a temporising bid to discover more about East's hand when they rebid. In this case it allows East to discover that West has a vital fifth Heart.

4NT is RKCN (1430) asking for Key Cards (4 Aces and ♥ K). 5♠ says I have two Key-Cards and I also have the ♥ Q

East knows the Key-Cards must be the Black Aces and can count 11 tricks. 

5NT is RKCB (1430) asking for the lowest King outside the Trump suit. 6♣ says I have the ♣ K

Now East can count 13 tricks and bids 7NT (without the ♣ K East settles for 6♥ )

Sometimes we are blind to the fact that we score better in a Major suit game than in No Trumps if we make more tricks in the Major suit. This is not our fault. Bridge players have long been prone to 3NT-itis. Here you can make 12 tricks in 3NT but only 11 in NT.

After a weak NT South's 2♥ shows five Spades and is a transfer. South's 3♥ then shows 4 Hearts and when North shows three Spades South should bid 4♠ .

Playing a strong NT then 1♦ - 1♠ - 1NT - 3♥ - 3♠ - 4♠ does the job.