The virtues of faith and hope pertain to knowledge, but love pertains to an act. Hence, love is the greatest:
By the virtue of faith we know what the Love of God is and that we and our loved ones are to live in It.
By the virtue of hope, we know that we will live in It and have our temporal needs provided for by the means that God will indicate and have our spiritual needs provided for by God directly through His Holy Catholic Church, which we know by faith was established by Him as the sole means of salvation.
By the virtue of love, we sacrifice ourselves to God for the salvation of ourselves and our loved ones, all ultimately for His glory.
To take this further, faith and hope are described as inferior since they will not exist in Heaven. In Heaven we will need not faith, as we will see God face to face and by faith we know that which we do not see. In Heaven there will be no hope, for we will already have attained salvation and by hope we know that which we have not yet attained. However, love remains, as the act performed in Heaven, a complete giving of self to God and receiving Him in turn, for all eternity, as an icon of the union between God the Father and God the Son, giving Themselves to Each Other, in an eternal union. The love that binds Them together as a single being is the Divine Holy Ghost and this is what is meant by the "Love of God". He, the Love of God, binds Father and Son; and likewise Christ and His Bride the Church in an icon of the Trinity; and likewise bridegroom and bride in an icon of both Christ and the Church and the Trinity.