God is the Supreme Being, and therefore, He is One. Inside God, there are three divine Persons, who are One God. Only one divine nature, but three divine Persons, possessing this one divine nature. In the gospel today, Jesus impresses on us His oneness with His Father. In their being, they are one. But more than that, Jesus teaches us, His followers, that we need to imitate this oneness with God. We achieve this by doing His Will, or by being united to His Will, like when Jesus prayed in Gethsemane, "...not my Will but Thy will done..." We pray, in fact, in the Lord's Prayer, "...Thy Will be done on Earth, as it is in Heaven..."
