Therefore leaving the principles of the doctrine of Christ, let us go on unto perfection; not laying again the foundation of repentance from dead works, and of faith toward God,
Therefore - Wherefore: seeing that ye ought not to be still 'babes' (Hebrews 5:11-14).
Leaving - getting further than elementary "principles." 'As in building, one must never leave the foundation; yet to be always labouring in "laying" it would be ridiculous (Calvin).
The principles of the doctrine, х ton (G3588) teen (G3588) archees (G746) logon (G3056)] - 'the word of the beginning;' i:e., the discussion of the first principles of Christianity (Hebrews 5:12).
Let us go on, х feroometha (G5342)] - 'let us bear ourselves forward:' with active exertion press on. Paul classifies himself with his Hebrew learners. Let us together press forward.
Perfection - the matured knowledge of those "of full age" (Hebrews 5:14) in attainments.
Foundation of - i:e., consisting in.
Repentance from dead works - namely, not springing from the vital principle of faith and love toward God, so counted, like their doer, dead before God. This repentance from dead works is therefore paired with "faith toward God." The three pairs of truths enumerated are designedly such as JEWISH believers might have partly known from the Old Testament, but had been taught more clearly as Christians. This accounts for the omission of distinct specification of some essential first principles of Christianity. Hence, he mentions "faith toward God:" not explicitly faith toward Christ (though included). Repentance and faith were the first principles taught under the Gospel.