There are so many areas to track quality in as well right: faith, belief, knowledge, action, word, heart, compassion, love, fruit etc...We've all met (and I've been) those men and women who call themselves followers of Christ but couldn't possibly be. Or those who are sold on social justice and clearly love people but never mention Christ or salvation or redemption. Or those who seem to have a real grasp on an authentic gospel lifestyle. How do we gauge quality?
John notes that others will know a true believer by their love (13:35). Jesus notes faith and obedience (8:31). A life lost and a cross carried according to Mark (8:34-38) - unfathomable ideas to those without the life of the Spirit in them. James notes faith and deeds (2:17)...and so on.
Love. It seems to be the common thread in the believers life. According to John God is love and according to Jesus if we really are disciples then He is in us and we are in Him...Love is in us and we are in Love. Love is the gauge or standard by which we define 'quality' of Christian.
This isn't to say we're able to rightly qualify a believers position in Christ. Only Christ knows the genuine state of His disciples. Though as fellow believers we're called to carry burdens, discipline, challenge, rebuke, correct, teach, train, account and judge (not eternally) the state of the body and in particular members when necessary.
This isn't a license to condemn I should mention.
I suppose overall we're all unworthy of the grace God offers. That said, we're not called to abuse His grace, quality of Christlikeness matters to Him most of all.
As Paul said...our attitude should be like Christs. Jesus is our standard and the Spirit is the quality control working through our hearts, the Word, and the Church.
Read Matthew 6:1-18 for a heart check on your actions and beliefs. Read Philippians 2:1-11 to check your attitude. Read the Gospel of John to breath in some fresh air.