A disciple of the Lord Jesus is someone who enters the narrow gate and walks the narrow path until they come to the end of the narrow path and are left with nothing but Christ. As you can see, this is a very, very narrow way, which is why few find it, and fewer still remain on it once they find it. Nothing of self can be retained. All of self must be lost in order to gain Christ.
As we walk the narrow way we are being changed from glory to glory. Today we should reflect a little more of the glory of God than yesterday; tomorrow we will reflect yet more than we did today. This is growth. Growth is not more knowledge or increase of years: it is simply more of Him and less of me. He increases as I decrease. This is what it means to be a disciple.