There are two matters to be discussed here: Division and Unity.
That there were various divisions already apparent in the church in Paul's day was well known as he discusses these at some length in the first three chapter of 1 Cor. Since then, divisions have multiplied and there is no sign yet that this will abate.
I am one that does not entirely regret such divisions. (Some are most unfortunate and have done a great deal of damage an history would be better off without them.) Divisions have created healthy discussions and clarified our thing on numerous topics as this very site demonstrates.
Despite the divisions, there are many parts of Christianity that are moving closer - again, this very site would been impossible just 60 years ago when many sections of Christianity refused to speak to one another. Now, at least, we are talking and with a common language of what the Bible actually says. If the church were homogeneous, no such discussion would have occurred.
Back to the text at hand, Eph 4:13. V13 should not be divorced from v11 & 12:
And it was He who gave some to be apostles, some to be prophets, some
to be evangelists, and some to be pastors and teachers, to equip the
saints for works of ministry and to build up the body of Christ,
until we all reach unity in the faith and in the knowledge of the
Son of God, as we mature to the full measure of the stature of Christ.
Note that Paul is essentially saying that the variety of gifts of the Spirit have been given to the church in order to built it (us, its members) up UNTIL it we reach "the full measure of the stature of Christ". Now, it is a simple matter of everyday experience that none of us has reached (either morally or sinlessly) the measure of Christ!! Such will only occur when the Lord returns and were are finally and fully perfected (see I Cor 15). Only at that time will we fully understand and be perfectly united.
BUT, until Jesus returns we need to continue to build each other up until that great day when we will understand and "not see through a glass darkly" 1 Cor 13:12.