I believe everyone has a definition but I'm glad to share this as taught by a spiritual authority i trust . I've at times seen activism being labelled as Christianity and I know we are called to be different from human rights activists.
If you want to to know what God describes as a mature christian, then i will give you a number of bible characters to shed the picture,not forgetting Romans 1:20(things here are a shadow of things above when you understand that scripture)
Doesn't it ring a bell how youthful parents tend to be so tough, as they age they tend to be loving and not as angry and beating you up as they used to be. Listen when Samson was a youth he knew how to fight and killed for the sake of the mission but in his last days he died for his mission although still the enemies died.
A man that has grown in God learns the art of being weak in God that his (God's)might, might rest upon him than being strong in him and nullify his strength that ought to Excell that of the arm of the flesh.
when Paul was Saul he was with the zeal and killed for God, and when he was of age he died by the hands of Nero for his God and mission hope you get the difference.
It reminds me of a new brother in salvation who was abusing the devil all sorts of words for the sake of Christ and the body it was a fun filled meeting.
Not forgetting Jesus who came as a lamb to be slaughtered yet some expected him to come as a lion to slaughter the Romans.
I mean when Moses was a youth he killed an Egyptian for his God and mission. God took him to the desert but at the end the Lord tells him to die and leave the mission behind not forgetting the enemies. God not Moses but God killed for Moses.
This I have seen many times, that there is a place where we get assignments and we own them more than the God who made them to us to the point that we can kill or even fight for them like peter pulled a sword to cut off someone's ear, the Lord respected him given the level of maturity of peter at the time but ladies and gentlemen either you receive this today or someday you will appreciate why the mature peter died for the Christ upside down on the cross.
Ladies and gentlemen, I said all of that to say Christianity is leaning on his power to save you not your own and believe he can do a better job turning the hearts of men, because he designed them anyway.
Christianity is believing that he will vindicate you, that they may see him in you, because he is the author and finisher of your faith.
Christianity is remembering that you accepted him because you couldn't save yourself and you needed him and living life like you actually do need him.