The Greek word here is homologeō and means “to say the same” and thus to agree in one’s statement. The word has strong legal connotations. A person can confess to a charge in court and thus openly acknowledge guilt. Or one may agree with a court order and thus make a legally binding commitment to abide by it. This last sense is implied in passages that call on us to acknowledge Jesus. We are to express our binding commitment to Jesus publicly and thus acknowledge our relationship to him as our Lord.