This:

For the mystery of lawlessness is already working. Only He who is now restraining him will do so until He is taken out of the way. Then the lawless one will be revealed, whom the Lord will consume with the breath of His mouth, and destroy with the brightness of His presence,

2 Thessalonians 2:7–8

Is this amplified:

Do not let anyone deceive you in any way. For that Day will not come unless a falling away comes first, and the man of sin is revealed, the son of destruction,

2 Thessalonians 2:3

Here is why. There is no object given to the Greek apostasia (falling away.) It means a falling away or abandonment, without an object one is assumed. Our English minds think leaving the faith, but that is not necessarily applicable here. It begs the question, falling away or abandonment from what and who or what is falling away?

That is when we must examine the immediate context. When we do, Paul amplifies what he is saying and provides greater detail. We get a clear idea that the abandonment is a “He” being removed.

The double-emphasis is just like Jesus saying, “Truly. Truly.”