A basic Biblical distinction more or less ignored by most Christian theologians is the difference between “the Gospel of the kingdom,” as emphasized in the Synoptic Gospels, and the “promise of eternal life,” as emphasized in John’s Gospel. 

Part of the kingdom gospel included the call to repentance. Since most theologians improperly mix the promise of life with the gospel of the kingdom, they conclude that repentance is also a requirement to have eternal life.  

Clarence Larkin, in his book Rightly Dividing the Word, clarifies that the gospel of the kingdom is not about personal salvation, and it included a call: 

When Jesus entered on His own ministry, His message was the same as John the Baptist’s—“Repent for the King of Heaven is AT HAND.” Matt 4:17. The repentance called for was a “NATIONAL REPENTANCE.” The Old Testament scriptures clearly teach that the Messianic Kingdom cannot be set up until Israel as a nation REPENTS…we are nowhere told that the “Gospel of the Kingdom” had anything to do with the salvation of the soul, and as it is to be preached again after the Rapture of the Church for a “witness” unto all nations, that the time has come for the setting up of the Kingdom (Matt 24:14) the inference is that the “Gospel of the Kingdom” has nothing to do with “salvation,” but is simply an announcement that the “Messianic Kingdom” is AT HAND (Larkin, Rightly Dividing, pp. 52-43, emphasis his). 

For more on the nature of repentance, see Bob’s book, Turn and Live: The Power of Repentance.