I don't know if that was his reason.
I don't know if Paul was aware of 1 John 3:9-10.
I do know that Paul gave the characteristics of men in the flesh, and of men in the Spirit, in Gal 5:19-25..."Now the works of the flesh are manifest, which are these; Adultery, fornication, uncleanness, lasciviousness,
20 Idolatry, witchcraft, hatred, variance, emulations, wrath, strife, seditions, heresies,
21 Envyings, murders, drunkenness, revellings, and such like: of the which I tell you before, as I have also told you in time past, that they which do such things shall not inherit the kingdom of God.
22 But the fruit of the Spirit is love, joy, peace, longsuffering, gentleness, goodness, faith,
23 Meekness, temperance: against such there is no law.
24 And they that are Christ's have crucified the flesh with the affections and lusts.
25 If we live in the Spirit, let us also walk in the Spirit."
Make your choice obvious to those around you.