Nodes decides if the transaction is valid before miners can get it. Miners can send back blocks to the nodes to be verified. The validity of the consensus is decided by the nodes because nodes are unable itself to make false transaction or in simple words, nodes can’t tell lies.
Full Nodes can verify the whole consensus of the blockchain. That’s why you need a power server for this as information in the blockchain will grow bigger and bigger.
Light Nodes only used relevant part of Full Nodes which you need. For example, sending and receiving money. Trust from both nodes is necessary because it sends and receives verification from full node back to lite node and vice versa