Bible Verses About Backsliding: Is departing form the simplicity of the gospel

¶ O foolish Galatians, who hath bewitched you, that ye should not obey the truth, before whose eyes Jesus Christ hath been evidently set forth, crucified among you?

This only would I learn of you, Received ye the Spirit by the works of the law, or by the hearing of faith?

Are ye so foolish? having begun in the Spirit, are ye now made perfect by the flesh?