To bear in mind is to keep something in your thoughts while you decide. Not forgetting the thing that changes the answer.
It is a set phrase and it takes a that-clause or a noun: bear in mind that he is new, bear in mind the cost. It is a polite way of introducing an objection, since telling somebody to bear in mind something is gentler than telling them they are wrong. Bearing in mind at the start of a sentence means taking that into account. Keep in mind is the American preference.
1phrasebear in mindTo remember and take something into account.
“Do bear in mind that the shop shuts at four.”
To bear something in mind is to carry it. The phrase joins bear, to carry or hold, to in mind, and dates from the first half of the sixteenth century, so remembering here is a load you keep with you.
Built from
From bear (“to carry; to hold”) + in mind. first half of 1500s.
Etymology from Wiktionary, CC BY-SA
Practised in Thinking & Memory, Common Word Pairs