"Whosoever therefore shall confess in Me before men, him will I confess also before My Father Who is in the heavens. But whosoever shall deny Me before men, him will I also deny before My Father Who is in the heavens." - Matthew 10:32, 33
St. John Chrysostom commenting on this passage writes:
"Mark Christ's exact care; He did not say that before men whosoever shall 'confess Me', but 'confess in Me' (εν Eμοι), showing how the confessor, not by a power of his own but by the help of grace from above, makes his confession. But of him who denies Christ before men, Christ said not 'whosoever shall deny in Me', but, 'deny Me'; for having become destitute of the gift, his denial ensues." ("Homily 34 On Matthew", PG 57:392)