In the Gospel of Mark, after Jesus spent 40 days in prayer he began his public ministry with a bold proclamation, "The time is fulfilled, and the kingdom of God is at hand; repent, and believe in the gospel" (Mark 1:15). He wanted them to convert, but used a particular word that has an added depth to it.
According to Andrew Greenwell, Jesus used the Greek word metanoia, which is usually translated in English as "repent." This word has a deep meaning, as Greenwell relates in an article on Catholic Online.
The verb metanoeo is a compound word formed by the joinder of the prefix meta, a preposition meaning "with" or "after," or even "beyond," and noieo, "I think." The verb metanoeo therefore means "I change my mind." Literally, then, metanoia is the state of thinking differently, a state where I have changed my mind, one occurring after some sort of encounter with reality.
Compendium of the whole Christian life
Pope Paul VI in his Apostolic Constitution Paenitemini, called these words of Jesus "a compendium of the whole Christian life" and further related the gravity of Jesus' choice of words.
The kingdom of God announced by Christ can be entered only by a "change of heart" ("metanoia") that is to say through that intimate and total change and renewal of the entire man—of all his opinions, judgments and decisions—which takes place in him in the light of the sanctity and charity of God, the sanctity and charity which were manifested to us in the Son and communicated fully.
The conversion that Jesus seeks is probably most exemplified by the parable of the Pharisee and the Tax Collector.
Two men went up into the temple to pray, one a Pharisee and the other a tax collector. The Pharisee stood and prayed thus with himself, "God, I thank thee that I am not like other men, extortioners, unjust, adulterers, or even like this tax collector. I fast twice a week, I give tithes of all that I get." But the tax collector, standing far off, would not even lift up his eyes to heaven, but beat his breast, saying, "God, be merciful to me a sinner!" I tell you, this man went down to his house justified rather than the other. (Luke 18:10-14)
Total conversion
In other words, Jesus seeks a total conversion of heart and not an external conversion that is expressed in external signs. To be truly converted we must, as Pope Paul VI noted, have a "total change and renewal of the entire man—of all his opinions, judgments and decisions."
When Jesus returned after his 40 days of prayer in the desert, he challenged his disciples to a conversion that was not on the surface level, but consisted of a complete change of life, a "metanoia."
It is a difficult challenge to accept, and likely will take a person's entire life to accomplish, but it is the type of conversion that Jesus seeks and asks us to embrace.
