His book THE LIFE OF MOSES is available from the Paulist Press in the series THE CLASSICS OF WESTERN SPIRITUALITY. The reader who is expecting a straightforward biography will be startled -- not necessarily disappointed. An example of his treatment is the following:
In Numbers 13 and 14 we read that when Moses had led the Israelites out of Egypt and to the borders of Canaan, he sent twelve spies into the land to look it over. They returned to report two things: (1) The inhabitants of the land were fierce warriors and would prove a formidable enemy. (2) The land was a good land, with fertile soil and an abundance of natural resources. As proof, they brought back a cluster of grapes so large that they hung it from a wooden pole that two men carried horizontally between them. Ten of the spies said that the enemy was too strong to be defeated, and that the Israelites ought to turn back, but the remaining two, Joshua and Caleb, urged the people to remember that the LORD was with them, and had shown Himself mighty to save. The people listened to the ten and prepared to turn back. At this the LORD was angry and said, "Very well, you shall wander in the wilderness for forty years, until all the men of this generation have died, except for Joshua and Caleb. Only then shall the next generation go in to possess the homeland that I promised to Abraham for his descendants." Hence the well-known child's nursery rhyme that goes in part:
Gregory (following the example of the Apostle Paul in 1 Corinthians 10) treats the Exodus as a type of our deliverance from the bondage of sin, and the Promised Land as a type of Heaven. He comments that the Israelites had been guilty of idolatry, of fornication, of repeated rebellions against Moses, of various disobediences to the commands of God, but that none of these moved God to deny them entrance into the Promised Land. It was only when they came to the Land, and God showed them what a good land He had prepared for them, and gave them a token of that goodness in the form of the cluster of grapes, hanging from a wooden pole between two spies, and they refused to trust in the promise of God to save them from their enemies, that they were turned back (indeed, that they turned themselves back). So, it is not failure to live virtuous lives that can keep us out of Heaven, but a refusal to believe in the mercy of God, and to trust His gracious declarations of His good will toward us, concretely expressed in the saving blood of Christ, Who is the True Vine, and Who for our sakes hung on the wood of the cross between two thieves, as the grape cluster hung on the wood of the pole between two spies, showing forth in His own Person the sign of God's good will to us and His assurance that He is ready to overcome all our enemies.
As you see, it is not really a biography of Moses, and it will not be to everyone's taste, not even to every Christian's taste. Clearly anyone who follows Gregory's example runs the risk of being led on a random walk by the will-o-the-wisp of his own imagination. But many Christians have received spiritual nourishment from this way of reading the Scriptures, and the example of St. Paul, as aforesaid, favors the view that this approach is at least sometimes of legitimate value.