Conclusion

Based on the grammar, historical background, and surrounding theology of the Eph. 2:14-15, it seems that the "dividing wall" is the relational division between Jews and Gentiles caused by the Law. Through Christ's perfect life and sacrificial death, he fulfilled the Law, making it no longer operative.  Without the Law to divide humanity, he was able to make the two groups, Jews and Gentiles, into one new humanity that would be reconciled to God for eternity.