How can a full node of a blockchain be quickly retrieved? I don't want to wait for bitcoin-core sync to complete.
Unless you have a fully synced copy of it already available on a another trusted machine, the "fastest" way to sync it is to just let Bitcoin Core sync "naturally"... There are other tips, like use an SSD to store the blockchain/chainstate data, if you have a lot of RAM set the "dbcache" value to at least half your total RAM size etc.Yes, it takes hours/days, but there really isn't any way to avoid it.
You also can use parameter "--assume-valid=[hex of most recent block]" to skip verifying script and slightly speed-up sync time.
As for it's security implication, check https://bitcoin.stackexchange.com/q/88652. TLDR : it's still considered safe.