Endurance, did you read the whole article? If you did then you would have notice the author quoted:
Matthew 5:17-20
17 "Do not think that I came to abolish the Law or the Prophets; I did not come to abolish, but to fulfill. 18 "For truly I say to you, until heaven and earth pass away, not the smallest letter or stroke shall pass away from the Law, until all is accomplished. 19 "Whoever then annuls one of the least of these commandments, and so teaches others, shall be called least in the kingdom of heaven; but whoever keeps and teaches them, he shall be called great in the kingdom of heaven. 20 "For I say to you, that unless your righteousness surpasses that of the scribes and Pharisees, you shall not enter the kingdom of heaven. NAS
The law includes the dietary laws and a plethora of other laws that do not apply to the New Covenant. The author has also ignored:
Hebrews 7:11-17
11 Now if perfection was through the Levitical priesthood (for on the basis of it the people received the Law), what further need was there for another priest to arise according to the order of Melchizedek, and not be designated according to the order of Aaron? 12 For when the priesthood is changed, of necessity there takes place a change of law also. 13 For the one concerning whom these things are spoken belongs to another tribe, from which no one has officiated at the altar. 14 For it is evident that our Lord was descended from Judah, a tribe with reference to which Moses spoke nothing concerning priests. 15 And this is clearer still, if another priest arises according to the likeness of Melchizedek, 16 who has become such not on the basis of a law of physical requirement, but according to the power of an indestructible life. 17 For it is witnessed of Him,
"Thou art a priest forever
According to the order of Melchizedek."
NAS
Now if someone chooses to observe the Sabbath, which is from sundown Friday to sundown Saturday that is fine, however it is not a sin or a rejection of God's truth to observe Sunday as a day of worship. This is especially true since the Sabbath was instituted as a day of rest not a day of worship.