Gregory, a man renowned for learning and behaviour, was promoted to the apostolical see of Rome, and presided over it thirteen years, six months and ten days. He, being moved by Divine inspiration, in the fourteenth year of the same emperor [maurice], and about the one hundred and fiftieth after the coming of the English into Britain, sent the servant of God, Augustine, and with him several other monks, who feared the Lord, to preach the word of God to the English nation. they having, in obedience to the pope's commands, undertaken that work, were, on their journey, seized with a sudden fear, and began to think of returning home, rather than proceed to a barbarous, fierce, and unbelieving nation, to whose very language they were strangers; and this they unanimously agreed was the safest course. In short, they sent back. Augustine, who had been appointed to be consecrated bishop in case they were received by the English, that he might, by humble entreaty, obtain of the Holy Gregory, that they should not be compelled to undertake so dangerous, toilsome, and uncertain a journey. The pope, in reply, sent them a hortatory epistle, persuading them to proceed in the work of the Divine word, and rely on the assistance of the Almighty.
(Bede, Ecclesiastical History, bk 1, ch. 23, as found at the Internet Medieval Sourcebook)
St Gregory's instructions on evangelization, written to Mellitus in 601, were among the most influential ever:
When Almighty God shall bring you to the most reverend Bishop Augustine, our brother, tell him what I have, after mature deliberation on the affairs of the English, determined upon, namely, that the temples of the idols in that nation ought not to be destroyed, but let the idols that are in them be destroyed; let holy water be made and sprinkled in the said temples - let altars be erected, and relics placed. For if those temples are well built, it is requisite that the be converted from the worship of devils to the service of the true God; that the nation, seeing that their temples are not destroyed, may remove error from their hearts and, knowing and adoring the true God, may the more familiarly resort to the places to which they have been accustomed.
And because they have been used to slaughter many oxen in the sacrifices to devils, some solemnity must be substituted for them on this account, as, for instance, that on the day of the dedication, or of the nativities of the holy martyrs whose relics are there deposited, they may build themselves huts of the boughs of trees about those churches which have been turned to that use from temples, and celebrate the solemnity with religious feasting, no more offering beasts to the devil, but killing cattle to the praise of God in their eating, and returning thanks to the Giver of all things for their sustenance; to the end that, whilst some outward gratifications are permitted them, they may the more easily consent to thee inward consolations of the grace of God.
For there is no doubt that it is impossible to efface every thing at once from their obdurate minds, because he who endeavors to ascend to the highest place rises by degrees or steps and not by leaps. This the Lord made himself known to the people of Israel in Egypt: and yet he allowed them to use the sacrifices which they were wont to offer to the devil in his own worship, commanding them in his sacrifice to kill beasts to the end that, changing their hearts they mad lay aside one part of the sacrifice whilst retained another: that whilst they offered the same beasts which they were wont to offer, they should offer them to God, and not to idols, and thus they would no longer be the same sacrifices.
Oh, and he wrote the Life of St Benedict :)