To participate in the transaction validation process, a minimum wallet balance (similar to a security deposit) needs to be maintained. Nodes participate in this Proof of Stake protocol to get rewarded for adding a new block of transactions to the blockchain. Although any random node may be selected for validating and adding a block to the blockchain, the size of the stake is directly proportional to the chances of that node being chosen to validate and add the next block. Adding the Proof of Stake protocol for mining prevents the miners from double signing or trying to attack the network. Doing so would lead to losing a part of their stake.
