⁵ Don’t you remember that when I was with you I used to tell you these things? 

내가 너희와 함께 있을 때에 이 일을 너희에게 말한 것을 기억하지 못하느냐

Starts with a negative participle which, put at the beginning of a Greek question, anticipates a positive answer.[1]

⁶ And now you know what is holding him back, so that he may be revealed at the proper time. 

저로 하여금 저의 때에 나타나게 하려 하여 막는 것을 지금도 너희가 아나니

‘What is holding him back’. ‘what is restraining him’ (ESV). ‘(저를) 막는 것’. ‘Him’ being the ‘man of lawlessness’, ‘the son of destruction’ in v.3. So before the last day of the Lord comes not only the identity of the evil power will be revealed, but also until then another power apparently far more supreme than the evil one holds it back from being revealed. The Thessalonians do remember and therefore know what or who is holding back the power of chaos and defiance and the purpose of such holding back.

⁷ For the secret power of lawlessness is already at work; but the one who now holds it back will continue to do so till he is taken out of the way. 

불법의 비밀이 이미 활동하였으나 지금 막는 자가 있어 그 중에서 옮길 때까지 하리라

In this verse the holding back is annotated to someone (grammatically masculine in Greek; 막는 자) where as it was to something (gram. neuter) in v.6. There are other possibilities that interpret this restrainer as the church or certain figures in history. The best option for this restrainer who Paul and the Thessalonians mutually understand and remember seems to be God himself (masculine) working through the Holy Spirit (neuter).[2] So two things are true just before/at the coming of the Lord: that the real face of the evil that has been deceiving people and defying God will be exposed and that until then God himself holds back its identity from being fully revealed. So, it is no wonder that we cannot quite point the evil power at work down to one thing.     

Lord thank you for your word that reminds us of the fact who is in true power running and sustaining this world. We think it would be better for us to know everything now. But you who know the best hold back some things until the end. In this way we know just enough to trust and follow you without being conceited or dismayed totally. Let us know and remember that you are the king of the whole universe and that you are good to us. Until you reveal things wholly, we live mixed and mingled in the world. Let us remain who we are in this mixture without being deteriorated into something else than a believer and a child of yours. Let us steadfast in seemingly good and bad things in life as your believer and child until you re-declare us worthy of you, you glorified in us. Praise be to your almighty name. Amen.  

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[1] οὐ (ou) ‘no’ (G3756) Negative Particle. no, not, not at all, in no way, absolutely not. At the beginning of a Greek question, it anticipates a positive response

[2] Blomberg, Craig L., and Darlene M. Seal. From Pentecost to Patmos, New Testament Introduction and Survey Volume 2,. London: APOLLOS, 2021, 228