bring, take, bring about
齎 centers on causing something to move from one place or state to another: bringing an object, taking something along, or bringing about a result.
齎 combines 齊 (likely phonetic) with 貝 (shell, money), suggesting bringing or supplying valuables. The exact historical development is uncertain.
The outer 齊 looks like a container or organized set, and 貝 inside is a shell (money). Picture carrying a box of valuable shells to bring or take somewhere.
For セイ, imagine you say 'say' as you bring a message: say -> セイ, and you bring the words along.