Is the Sabbath now a Saturday or a Sunday?
It is neither!
The various arguments in favour of Saturday versus Sunday observance of a weekly Sabbath are spiritually sterile and completely misleading, since as we have just seen, the New Testament Sabbath is an every day rest.
The special Sabbath-feast days of Leviticus 23 were ‘types or shadows’, of greater things to come. Passover speaks of Christ our Redeemer, and the Feast of the Firstfruits speaks of Christ risen from the dead; Pentecost points to the outpouring of the Holy Spirit on the Day of Pentecost; the Day of Atonement looks forward to the Great High Priest, Jesus, the Son of God. Just so, the Old Testament pattern of a weekly Sabbath, in which Israel was to remember their Creator and Redeemer, foreshadowed that greater and complete rest into which we enter when we receive the promise of the Holy Spirit.
This is why Paul warns the Colossians: (Colossians 2:16-17 RSV) "Therefore let no one pass judgment on you with regard to a festival or a new moon or a Sabbath. These are only a shadow of what is to come; but the substance belongs to Christ".
Paul’s exhortation is not to chase shadows (such as Sabbaths), but seek the substance, which is Christ!