Some Answers (see part 1 first)
Keeping the seventh-day Sabbath is one of the ten commandments, not a tradition of man. Remember what Paul said.
"What shall we say then? Is the law sin? God forbid. Nay, I had not known sin, but by the law: for I had not known lust, except the law had said, Thou shalt not covet."
—Romans 7:7
If we say, "the sabbath only existed after mt. Sinai", we deceive ourselves because clearly the 10 commandments were in effect before that. Adam and Eve knew it was a sin to disobey God, Cain knew it was a sin to kill, Joseph knew that adultery was a sin plus many other instances.
A common misconception is that the Sabbath was only for the Jews. All faithful Christians today are Jews spiritually speaking.
Not as though the word of God hath taken none effect. For they are not all Israel, which are of Israel: 7 Neither, because they are the seed of Abraham, are they all children: but, In Isaac shall thy seed be called. 8 That is, They which are the children of the flesh, these are not the children of God: but the children of the promise are counted for the seed.
—Romans 9:6–8
He came to His own, and His own did not receive Him. But as many as received Him, to them He gave the right to become children of God, to those who believe in His name.
—John 1:11-12
For he is not a Jew who is one outwardly, nor is circumcision that which is outward in the flesh. But he is a Jew who is one inwardly; and circumcision is that which is of the heart, by the Spirit, not by the letter; and his praise is not from men, but from God.
—Romans 2:28,29
For you are all sons of God through faith in Christ Jesus. For as many of you as were baptized into Christ have put on Christ. There is neither Jew nor Greek, there is neither slave nor free, there is neither male nor female; for you are all one in Christ Jesus. And if you are Christ's, then you are Abraham's seed, and heirs according to the promise.
—Galatians 3:26-29
If we say the Sabbath is done away with and only nine remain, remember…
For whosoever shall keep the whole law, and yet offend in one point, he is guilty of all.
—James 2:10
God's character is located in the 10 commandments and if they were changed it would mean that God has changed. If we say "Christ changed the Sabbath" remember these…
" Jesus Christ is the same yesterday and today and forever."
—Hebrews 13:8
"For I, the LORD, do not change;"
—Malachi 3:6
"Every good gift and every perfect gift is from above, and cometh down from the Father of lights, with whom is no variableness, neither shadow of turning."
—James 1:17
“God is not a man, that He should lie,
Nor a son of man, that He should repent;
Has He said, and will He not do it?
Or has He spoken, and will He not make it good?"
—Numbers 23:19
"Hast thou not known? hast thou not heard, that the everlasting God, the LORD, the Creator of the ends of the earth, fainteth not, neither is weary? there is no searching of his understanding."
—Isaiah 40:28
