The standard definition of a friend is someone who shares the same values and interests as you and perhaps someone who is part of your history (someone you have grown up with).
As christians it is important to have christian friends, people that sees life the same way as you. Even with christian friendship, it is important to have decreeing spirit because it is not everyone that says Lord Lord truly loves the Lord.
There are 3 types of Christian Friendship;
1) Mentor Friendship: In a mentoring relationship, we teach, counsel, disciple other Christian friend. This relationship is based on ministry, similar to Jesus and his boys.
2) Mentee friendship: In this relationship we are the ones being taught, counseled or disciples. We are on the receiving end of ministry.
3) Mutual friendship: This type of friendship is not based on mentoring. In these situations, the two individuals are usually more aligned on a spiritual level, balancing the natural flow of giving and receiving between genuine Christian friends.
Importance of having Christian friends
1) they encourage you positively and not in pursuits that are not good for you.
2) they ask difficult questions - when you are struggling and a friend asks how you are, it can be tempting to say "fine". Godly friends don't let you get away with this, they ask difficult questions to find out how you really are, how they can help you and how they can pray for you.
3) they offer Godly counsel - advice is easy to come by these days, but Godly friends give you advice based on scripture that you can trust and their advice takes into consideration your unique circumstances.
4) they keep you accountable - when you are slipping, back sliding, missing church, Bible study or perhaps misbehaving - they will draw you back.
5) they pray with you and for you.
6) they have the resources you need - none of us has all the answers, but we can band together. Not only do Godly friends offer the advice, accountability and prayers, but they connect you with other resources. Even if it is has simple as "Need a ride to church this Sunday?".
There is nothing wrong with having *non Christian* friends, but you must be discerning when cultivating quality friendships. Have a mix of both - with your non Christian friends there is a real unique opportunity to evangelise and for God to use you to reach unbelievers by testimony. Don't shy away from non Christian - remember the great commission!
The bible says a lot about friendship; see bellow;
1 Corinthians 15:33 "bad company will corrupt good character"
Ecclesiastes 4:9-12 "two are better than one" and goes on to tell how life is much better when you have a friend
Proverbs 13:20 "Whoever walks with the wise becomes wise, but the companion of fools will suffer harm".
Proverbs 17:9 "Whoever covers an offense seeks love, but he who repeats a matter separates close friends".
Romans 1:12 "That is, that we may be mutually encouraged by each other's faith, both yours and mine."
Proverbs 27:6 "Faithful are the wounds of a friend; profuse are the kisses of an enemy"
Proverbs 27:17 "Iron sharpens iron, and one man sharpens another".