“No one after lighting a lamp puts it in a cellar or under a basket, but on a stand, so that those who enter may see the light.” (Luke 11:33)
"Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all that I have commanded you. And behold, I am with you always, to the end of the age.” (Matthew 28:19-20)
Your misapplication of this verse to justify keeping what is a supposedly the One, True Church a hidden little ethnic club was all too typical of my experience among the Orthodox, particulalry the cradle Orthodox. I remember one woman basically telling me that Orthodoxy is too precious to share and that it should be hard to find. Which of course is the antithesis of the Gospel. This lack of universality is a screaming testimonial that Orthodoxy does not bear an essentially mark of being exclusively the one, true church.
Catholic churches operated the same way when first built in the U.S.: e.g. St. Stanislaus (Polish parish), St. Patrick (Irish parish), St. Anthony of Padua (Italian parish), St. Boniface (German parish), St. Elizabeth (Hungarian parish), etc. Even today, there are Catholic (and Protestant) churches that still show these roots. There is nothing wrong with ethnicity. People of similar ethnicity often have similar culture, and similar ways of expressing themselves. The problem is not with ethnicity, but exclusion on that basis. No Catholic has any real objection to 95+% of the Roman Popes, supreme bishops of the Universal Church, being Italian.
So you heard something off from an Orthodox lady.
I once heard a Catholic lady say “We have a lot to learn from the Protestants” (in the context of worship). I thought that was a little off, but I certainly couldn’t say she was a model of the Catholic attitude. It was her personal opinion, with which I disagreed.
Many Orthodox Churches hold events open to the public (Greek festivals, Slavic festivals, open house, miraculous icons, etc.) At these events, the priest gives tours of the church, explaining to the group the Orthodox Faith. A few weeks ago I went to a Greek church during a festival. Inside the nave, traditional Mennonites were walking around, gazing at the iconography. I was told that several Mennonites in the area had converted to Orthodoxy.
My priest actively lectures at the local college on the Orthodox interpretation of Scripture. And if people are near completely unaware of Orthodoxy, they cannot help but wonder about those onion-domed structures and the shaggy, black-robed fellows who walk in and out of them–not to mention the hint of frankincense on the air. The light is there for all to see. People just have to come in to see it.
The Orthodox Churches in the U.S. are active with OCMC, which sends missionary priests to all over the world, including several places in Africa that hitherto have not known Orthodoxy.