このことをよく覚えておきなさい。

this (something or someone close to the speaker (including the speaker), or ideas expressed by the speaker)

thing; matter; incident; occurrence; event; something serious; trouble; crisis; circumstances; situation; state of affairs; work; business; affair; after an inflectable word, creates a noun phrase indicating something the speaker does not feel close to; nominalizing suffix; pretending to ...; playing make-believe ...; alias; aka; nickname; alternative name; also known as

indicates direct object of action; indicates subject of causative expression; indicates an area traversed; indicates time (period) over which action takes place; indicates point of departure or separation of action; indicates object of desire, like, hate, etc.

nicely; properly; well; skillfully; skilfully; frequently; often

to memorize; to memorise; to commit to memory; to learn by heart; to bear in mind; to remember; to learn; to pick up; to acquire; to feel; to think; to regard

to do