I think in the context of being a disciple of Jesus, maturity comes from trying to establish that habits, heart posture, and actions of Jesus in your life. For this looking to the four Gospels would be a good start, as well as a lot of Paul’s letters. I think along with that Maturity means knowing, and accepting that you are not perfect and will not be perfect every day, and that is okay. Jesus does not expect or call us to be perfect. He only calls us to be persistent in our walk with him. When we fall or stumble, we come before God and acknowledge our shortcoming, repent, and accept the forgiveness, grace and mercy he has for us that we do not deserve. For it is not by works, but out of Mercy we are saved. I read a passage of scripture this morning in the book of Titus. Titus 3:5 “he saved us, not because of righteous things we had done, but because of his mercy. He saved us through the washing of rebirth and renewal by the Holy Spirit” So in the context of mature face, I think it is the ability to humble yourself before God, and ask yourself in the mirror “Am I becoming more like Jesus?”