The Day Of The Lord vs. The Lords Day

I was engaged in a conversation earlier with a Pastor of a friend. He was insisting that we should worship on "the Lord's day!" I asked when that was, he said "Sunday." I pointed out that every single time "the Lord's day, or the day of the Lord" was mentioned, it speaks of utter devastation! He argued that I was in error. So we took a quick stroll through Scripture. Wail, for THE LORDS DAY is at hand! It will come as destruction from the Almighty... Every man's heart will melt, and they will be afraid...Behold, THE LORDS DAY comes, cruel, with both wrath and fierce anger, to lay the land desolate; and He will destroy its sinners from it. For the stars of heaven and their constellations Will not give their light; The sun will be darkened in its going forth, And the moon will not cause its light to shine. "I will punish the world for its evil, and the wicked for their iniquity;(Isaiah 13:6-13). Alas, for THE LORD'S DAY is near, and it comes as destruction from the Almighty! Blow the trumpet in Zion and sound an alarm in my set-apart mountain! Let all the inhabitants of the earth tremble, for the day of יהוה is coming, it is near! (Joel 1:15 & 2:1) Hush! In the presence of the Master יהוה! For the LORDS DAY for YAHWEH has prepared a slaughter! And it shall be, in the day of slaughter of YAHWEH that I shall punish the rulers and the sons of sovereigns... (Zephaniah 1:7-8) The sun shall not give it's light and the moon will turn into blood, before the great and terrible day of THE LORD. (Joel 2:31 & Acts 2:20) For you yourself know very well that THE LORDS DAY comes as a thief in the night! (1Thes 5:2) He piped up and said, "John was caught up in the Spirit on SUNDAY!" I said, "no, he was in a vision of THE LORDS DAY It is the exact same day as all the other Prophets spoke of. The entire purpose of Revelation is John describing his vision of the return of our Messiah. It is not going to be pretty. Perhaps we should worship on the Sabbath as commanded, it is carved in stone after all." Suddenly the conversation was over. Until a bright light went off in his head... "But Acts 20.7 tells us plainly that they gathered to worship on the first day of the week, Sunday" he continued I felt bad because I once believed what I read without actually STUDYING to show myself approved. So I kindly replied "Thankfully, some of the newer translations have corrected King James error on this verse...... this verse has ADDED ONE WORD that's displayed in italics, meaning the word is NOT DIVINE SCRIPTURE but man's opinion" He was looking at his Bible when he noticed the italics of the word... DAY..... and even he knew the end of his theory was near. When you remove the word DAY.... and you look at the meaning of the word WEEK, the very next word... what do you find? I patiently asked him He replied "sabbaton".... I continued....."MEANING SABBATH, CORRECT?" CRICKETS I kindly continued "Now, look at the word FIRST...as in FIRST DAY of the week" it means ONE SO, LET'S SEE WHAT ACTS 20.7 truly says "THE DISCIPLES (60 YEARS AFTER CHRIST REPLACED THE SABBATH) gathered on ONE OF THE SABBATHS." "STUDY to shew thyself approved unto Yahweh, that you might not be ashamed"