5♣ is the only makeable game (without help from the defence) and this auction is a sensible way to reach it.

After East rebids 2♣ West's hand increases in value considerably because of the ruffing value of the Diamond void. West is at least worth an invitational raise to 4♣ . Since West has a Losing Trick Count of six then a direct raise to 5♣ would not be wrong (assuming partner has a Losing Trick Count of 7 for their opening bid) but with all your strength in one suit I think caution is called for.

East is stronger than minimum and has fewer Losing Tricks than partner has assumed so should not hesitate to accept the invitation and bid 5♣ .

Three pairs made 3NT on this hand which they had no right to. The defence won't lead a Diamond or a Heart as those suits would have been bid. That leaves a choice of Clubs or Spades and it is a good maxim when defending against No-Trumps and having a choice of attacking a Major or Minor suit to choose the Major. This is because the declaring side are likely to bid a Major suit if they have one.

Although South won't have led a Diamond, North must seize the moment and switch to a Diamond when they see West is void in the suit. That sets up three Diamond tricks to be taken when South gets in with the ♣ K which they must do before declarer can come to nine tricks. 

"Par" is an important concept at Pairs and this hand illustrates it perfectly.

N-S have a 'Par' score for each hand which is the best result they can get if the opponents don't bid. On this hand nine tricks in a Heart part-score for +140 is the best they can do,

E-W also have a 'Par' score on each hand. On this board ten tricks in a minor suit part-score (Clubs or Diamonds) for +130 is the best they can do in an uncontested auction.

The hand also has an overall 'Par' contract beyond which if either side bids they will get a worse score than by Passing.

On this hand when North bids 2♥ E-W will score -140 if East Passes but will score +130 if East bids 4♦ .

If North now Passes 4♦  N-S will score -130 but will get a better score ( -50 ) if North bids 4♥ .

4♥ by North is the overall 'Par' for this hand. If E-W bid 5D they will turn +50 into a worse -50 and if N-S bid 5♥ they will turn -50 into a worse -100.

Spotting the absolute Par for a hand is key to successful competitive bidding and well done to all five pairs for playing in the Par contract.