In the third chapter of the Book of Tobit, we are introduced to the unfortunate Sarah,  widowed seven times.  In his commentary on this book, St. Bede explains:

" 'Sara, the daughter of Raguel, of a city of the Medes, was given to seven husbands, and a demon killed them as soon as they went into her.'  This denounces, in figure, the crowd of the nations, all of whose teachers knew only the life of this world, which is denoted by "seven days", but knew nothing, and so did not teach, of eternal life. Therefore, they were seized by the devil, inasmuch as they were delivered up to idolatry, until the coming of our Lord, the True Spouse, who joined himself to his Bride through faith after overcoming the enemy.  [This is signified when] Tobiah took Sara as his wife after the demon had been bound, by the command and assistance of the archangel.  Not unfittingly, the divinity of our Savior is signified [by the archangel], just as his humanity is signified by Tobiah.  

The seven previous husbands, then, represent the philosophers and teachers of the ancients who, however learned in the matters of this world, were ignorant of spiritual matters and so were unworthy of Sara, who signifies the people of God awaiting his advent.  This marriage of Christ and humanity, accomplished in the Lord's Incarnation and consummated in his Passion, is to be celebrated in heaven by the angels and saints together, at the wedding feast of the Lamb.