The Greek phrase ei mē combines the conditional particle ei ('if') with the negator mē ('not') to mean 'if not,' 'except,' 'unless,' or 'but only.' It is one of the most common exceptive constructions in New Testament Greek, appearing hundreds of times to introduce the sole exception to a universal statement.
The theological importance of ei mē is enormous when applied to Christ. John 14:6 uses the construction implicitly: 'No one comes to the Father except through me.' Acts 4:12: 'There is no other name under heaven given to mankind by which we must be saved.' These ei mē constructions establish the exclusivity of salvation through Christ.
Conversely, ei mē also marks God's unlimited grace: Romans 11:15 speaks of the acceptance of Gentiles except through Israel's rejection. The word that makes grace universal by exception is the same word that makes salvation particular: Christ alone is the gateway.