expression
first of all; to begin with; in the first place
Used to introduce the most important point or the first step in a sequence. Often appears at the beginning of a sentence or clause.
まず第一に、健康が一番大切です。
First of all, health is the most important thing.
まず第一に、予算を確認しましょう。
To begin with, let's check the budget.
Combination of まず (first, to begin with) and 第一に (firstly, primarily). The phrase is a straightforward compound emphasizing the foremost point.