To “consecrate” oneself “to service in the Cause of God” – ‘Abdu’l-Baha explains its meaning

As to the terminology I used in my letter, bidding thee to consecrate thyself to service in the Cause of God, the meaning of it is this: limit thy thoughts to teaching the Faith. Act by day and night according to the teachings and counsels and admonitions of Bahá'u'lláh. This doth not preclude marriage. Thou canst take unto thyself a husband and at the same time serve the Cause of God; the one doth not preclude the other. Know thou the value of these days; let not this chance escape thee. Beg thou God to make thee a lighted candle, so that thou mayest guide a great multitude through this darksome world. (‘Abdu’l-Baha, ‘Selections from the Writings of `Abdu'l-Baha’, p.100)