Why does believing in the resurrection imply that Christ died?

Resurrection necessarily presupposes death: one cannot be raised from the dead unless he first died. So believing God raised Christ from the dead carries the implied confession that Christ actually died; Scripture then joins that belief with His burial and resurrection to the promise, "Thou shalt be saved."

Les explains that the verse speaks of believing in the heart that God raised Him from the dead, then points out that this implies death, because He could not have been raised unless He had died. The context expands the confession to Christ died, was buried, and rose again, and connects that faith to the promise "Thou shalt be saved." Les also notes that confessing with the mouth the Lord Jesus goes beyond His earthly ministry, since He had not yet died then; after the cross and resurrection He becomes Lord.

Romans 10:9

That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved.

Why does believing God raised Jesus imply that He also died and was buried?

Resurrection from the dead necessarily presupposes a prior death, since God could not raise Jesus from the dead unless He had died. Burial is likewise implied in the sequence of Christ's death, burial, and resurrection. Believing God raised Him therefore includes the implied facts of His death and burial, with salvation promised.