The gospel must be central because nothing else even comes close to filling the eternal gap.
We all agree that fallen man has a "God-shaped hole," but then we go on to suggest all kinds of fillers that are not God -- financial success, good sex, promotions at work, healthy relationships, happy spouses and children, community service, outlets for our creativity, etc. All good things but all things you can have and do and still be eternally bankrupt.
Our scale is far too small. The Bible speaks to all manner of good things useful to all men, but the Church is starving (starving!) for the glory of God. We too easily forget that the gospel covers the scale of eternity, that it is the division between real life and death, that God is infinite and our sin is a condemnation-worthy offense against an eternally holy God. We preach and we settle for much less than, "Oh, the depth of the riches of the wisdom and knowledge of God!"
Every week people file into our church services aching for eternity; in our zeal to provide something they may find comfortable and useful and inoffensive, are we offending the God who wishes to offend us in awe of his glory? Are we dismissing our brother Jesus whose formula for victory includes crucifixion?
The scale is enormous, the stakes are high. Instead of spiritually dressing up the idols we know people want, let's give them what they need -- God all in all, the filling of the Spirit, the exaltation of the risen Lord.
Behold what manner of love the Father has given unto us, that we should be called the sons of God!
-- 1 John 3:1a
That should be the chief service of our worship services -- beholding. Behold our glorious God and his lavishing of grace on us in his precious Son.
For from him and through him and to him are all things. To him be the glory forever! Amen.
-- Romans 11:36