Gospel-Centered or Christ-Centered?

Being gospel-centered isn't the same as being Christ-centered. We are to move on from elementary truths of milk to meat. The Gospel, while the good news of salvation, is not what we feed on for the rest of our lives. We feed on the whole counsel of the Word and that necessarily means all the doctrines that mature us. That means hard, deep truths of Scripture. And all of them are knowable which is why they are powerful to equip us for every good work (2 Tim. 3:16-17). I suspect that the popular notion of "gospel centered" is a way to keep Christians immature. We are to grow up in all things in Christ. A great book on this is Ephesians. It teaches a treasure trove of deep doctrine and how it helps in our sanctification. We cannot be sanctified without biblical doctrine (anyone who tells you that, who makes a false dichotomy between doctrine and practice isn't being honest to the Word).

Heb 5:11 Concerning him we have much to say, and it is hard to explain, since you have become dull of hearing.
Heb 5:12 For though by this time you ought to be teachers, you have need again for someone to teach you the elementary principles of the oracles of God, and you have come to need milk and not solid food.
Heb 5:13 For everyone who partakes only of milk is not accustomed to the word of righteousness, for he is an infant. 
Heb 5:14 But solid food is for the mature, who because of practice have their senses trained to discern good and evil.

Heb 6:1 Therefore leaving the elementary teaching about the Christ, let us press on to maturity, not laying again a foundation of repentance from dead works and of faith toward God,

Eph 4:1 Therefore I, the prisoner of the Lord, implore you to walk in a manner worthy of the calling with which you have been called, 
Eph 4:2 with all humility and gentleness, with patience, showing tolerance for one another in love,
Eph 4:3 being diligent to preserve the unity of the Spirit in the bond of peace.
 Eph 4:4 There is one body and one Spirit, just as also you were called in one hope of your calling;
Eph 4:5 one Lord, one faith, one baptism,
Eph 4:6 one God and Father of all who is over all and through all and in all.

Eph 4:11 And He gave some as apostles, and some as prophets, and some as evangelists, and some as pastors and teachers,
Eph 4:12 for the equipping of the saints for the work of service, to the building up of the body of Christ;
Eph 4:13 until we all attain to the unity of the faith, and of the knowledge of the Son of God, to a mature man, to the measure of the stature which belongs to the fullness of Christ.