Ephesians is a letter for the Christian church (a variety of home churches of people from a variety of backgrounds). Ephesus had a large amount of variety in religious backgrounds and beliefs. From Introduction and Background: Paul's Letter to the Ephesians,
"Ephesus was pluralistic in every way. Many ethnic and cultural
backgrounds were represented, and religious pluralism was entrenched
This letter's aim is not converting Jews to Christianity, but guiding new Christians of eclectic backgrounds.
"[H]e does write into a culturally chaotic, temptation-laden
environment in which his implied purpose is to instruct and encourage
Ephesian believers in their calling to unity as the Body of Christ,
both Jew and Gentile, and in their growing in Christian maturity." (ibid.)
The emphasis on 'one' at Ephesians 4:5 is similar to Paul's statement at Galatians 3:27-28.
"For all of you who were baptized into Christ have clothed yourselves
with Christ. 28 There is neither Jew nor Greek, slave nor free, male
nor female, for you are all one in Christ Jesus."
For the Christians in Ephesus, they need to recognize they all have one Lord, one faith, and one baptism. They are all one in Christ. This says nothing directly about whether the Mosaic Covenant is still binding on certain people (i.e., Jews who have or have not converted to Christianity).
Compare Hebrews 8:13.
"By speaking of a new covenant, He has made the first one obsolete;
and what is obsolete and aging will soon disappear."
'Will soon disappear' means it still exists. When will it disappear? AD 70, with the destruction of the Second Temple, is an obvious possible point.
Compare Matthew 5:18.
"For I tell you truly, until heaven and earth pass away, not a single
jot, not a stroke of a pen, will disappear from the Law until
everything is accomplished."
Jesus is saying the Law will be upheld until 'heaven and earth pass away'. When does that happen? For many preterists, an obvious date is AD 70, with the destruction of the Second Temple.
Similarly, Matthew 24:34-35.
"Truly I tell you, this generation will not pass away until all these
things have happened. 35 Heaven and earth will pass away, but My words
will never pass away."
There is a straightforward interpretation of these lines. Heaven and earth will pass away within 'this generation'. That is within about 40 years after Jesus spoke the words. AD 70 is in that range (general consensus is Jesus was crucified in AD 33).