teknonoftheos should believers in God who call themselves Christian keep the Law, the whole Law, all the mitvouth - reportedly at least 613?
Yes, although differently in the new covenant, because there was a change in priesthood when Yeshuah became high priest, where one example of a difference in how Torah is obeyed differently are the festivals and the Shabbat, where the requirement to observe these set-apart days is fulfilled by observing the reality they foreshadowed, such as,
Fulfilling the Passover through the Messiah, since he became the literal passover lamb.Fulfilling First Fruits through Yeshuah, since he was resurrected on First Fruits. This is a spring festival that was fulfilled in the first coming of Yeshuah.
Fulfilling the Feast of Weeks (Pentecost) by receiving the set-apart airflow, since the body is now the new place where God has chosen to place his name, for worship. This is a spring festival that was fulfilled in the first coming of Yeshuah.
Fulfilling the Festival of Trumpets through the second coming of Yeshuah, where the seven trumpets of Revelation will be blasted beginning in Tishri 1, in fulfillment of the festival.
Fulfilling the Day of Atonement in Tishri 10 through the second coming of Yeshuah, where the dead are raised in Yeshuah and are transformed into new bodies.
Fulfilling the Feast of Tabernacles in Tishri 15 through the second coming of Yeshuah, where the seven bowls of wrath of Revelation are poured for seven days, for aside from living in tabernacles, the festival also required the pouring of wine on the altar each day for seven days as a liquid alcoholic offering.
And finally, fulfilling the Shabbat by entering the thousand year rest of Yeshuah, which is what the seventh day foreshadowed, the last one thousand years of the full seven thousand years for this heaven and earth.
And this is why according to Paul, it no longer matters to observe these festivals, not because the requirement to observe them has been nullified, because "until heaven and earth passes, not one jot or one tittle will fall from the Law until everything is accomplished", but because the way these festivals are observed in the new covenant has changed, through the realities found in Yeshuah that each festival foreshadowed. And once all festivals and also the Shabbat are fulfilled, which will be at the completion of the last one thousand years of this heaven and earth, then the entire Law will be fulfilled, and it shall pass, along with this heaven and earth.