....”we have seen the true light, we have found the true faith....” ....
IMHO, that’s one of the prayers in the Divine Liturgy that one cannot understand unless one has received [Orthodox] Holy Communion!!!!
I'd temper that by stating "one cannot FULLY understand..."
There is a gradual awakening with inquirers, a steady recognition that Orthodoxy is the true faith, which then is overcome with a yearning to be able to "taste the fountain of Immortality". And when that blessed day of personal Pentecost that is the Sacrament of Chirsmation arrives, then the fullness of that canticle truly fills one's mouth with God's praise!