3 "Different" Terms in the NT Describing Salvation

Interesting, the New Testament (NT) presents salvation by using quite different terms/words. The theme/key phrase of:

• The synoptic gospels of Matthew, Mark and Luke is "the kingdom of God/heaven."
• John's gospel is "eternal life" (with infrequent use of the phrase "the kingdom of God).
• Paul's 13 epistles is "grace" or "the gospel," both of which emphasizes "justification by faith" (while very infrequently using the above 2 phrases in the gospels).

What might be the significance of this?

• If we focus on the synoptic gospels and "the kingdom of God" we tend to be activist Christians (focusing on discipleship and/or mercy ministry). 
• If we focus on John's gospel and "eternal life" we focus on having a "real" and authentic life as Christians.
• If we focus on Paul's epistles and "grace" we incline toward theology and sound biblical doctrine.

This might be an oversimplification. Nonetheless, how might we apply this? Over-studying or over-emphasizing one area might skew/bias our Christian expression, while the Bible contains "the whole counsel of God" (Acts 20:27). These 3 expressions of salvation seems to be in keeping with Jesus' words in the great command (Mt 22:37; Mk 12:30) where Christians are to:

• love God with all our strength by advancing "the kingdom of God."
• love God with all our heart with deep intimacy and authenticity.
• love God with all our mind with deep thought, reflection, depth and understanding.