The Father's holy spirit. But this is beside the point. He was being saved, not already saved per what he thought of himself. This has more to do with physical harm too.
15:2 δι᾽ οὗ καὶ σῴζεσθε τίνι λόγῳ εὐηγγελισάμην ὑμῖν εἰ κατέχετε ἐκτὸς εἰ μὴ εἰκῇ ἐπιστεύσατε
[1Co 15:2 KJV] 2 By which also ye are saved, if ye keep in memory what I preached unto you, unless ye have believed in vain.
Inflected:
σῴζεσθε Root:σῴζω
Strong's:
G4982English :ye are saved (
actually, ye are being saved), Code:V-PPI-2PLong:Verb - Present Passive Indicative - 2nd Person Plural
Notice it is present passive.