In our spiritual life we are asked to continually grow becoming more and more like Christ. Saint Basil the Great tells us that if we are advancing in virtue we are ever changing. This change involves an inner change. This is a change that affects our attitude towards the world, our friends and our enemies, our entire world view.
'When I was a child' it is said, I spoke as a child, I felt as a child, I thought as a child. Now that I have become a man, I have put away the things of a child' (1 Cor. 13.11) Again, when he had become a man, he did not rest from his work, but 'forgetting what was behind, he strained forward to what was before, he pressed on towards the goal to the prize of the heavenly calling' (Cf. Phil. 3.13, Cf. n. 10 supra.) There is a change, therefore, of the inner man who is renewed day by day.... This inner change does not come to just any one. It comes to one who is seeking change, one who seeks the love of God each and every day. It is change where we are participants, where we have to make use of our free will, and to discipline our mind and body. It is change that involves a shift in the orientation of our heart.
Saint Basil writes,
It is not the privilege of any chance person to go forward to the perfection of love and to learn to know Him who is truly beloved, but of him who has already 'put off the old man, which is being corrupted through its deceptive lusts, and has put on the new man' (Eph. 4.22, 24) which is being renewed that it may be recognized as an image of the Creator. Moreover, he who loves money and is aroused by the corruptible beauty of the body and esteems exceedingly this little glory here, since he has expended the power of loving on what is not proper, he is quite blind in regard to the contemplation of Him who is truly beloved. He is saying that we need to make sure that our motivations are not about the love of money, our the glamorization of our physical looks, or our accomplishment and recognition in worldly affairs. Instead the change we seek is only about the "perfection of love" towards our God. Our effort is to be direct towards the commandment of our Lord: 'Thou shalt love the Lord thy God with thy whole heart, and with thy whole soul, and with thy whole mind.' (Mark 12.30) Saint Basil helps us understand the meaning of "whole heart." It has to do with being a true friend of God.
The expression, 'With thy whole,' admits of no division into parts. As much love as you shall have squandered on lower objects, that much will necessarily be lacking to you from the whole. Because of this, of all people few have been called friends of God, as Moses has been described as a friend; (Cf. Exod. 33.11) likewise, John: 'But the friend' he says, 'of the bridegroom, who stands, rejoices exceedingly,' (John 3.29) that is to say, he who has a steadfast and immovable love for Christ, he is worthy of His friendship. WHo is a friend? "He who has a steadfast and immovable love for Christ." True friendship is based on true love. WHen we love someone we are continually seeking to be with them and to please them. Being a friend of God means we seek Him above all else and desire with our whole being to please Him, doing His will. It is the Lord's disciples that we can see as models for this true friendship.
Therefore, the Lord said to His disciples who were already perfect: 'No longer do I call you servants,' but friends; 'because the servant does not know what his master does.' (John 15.15) Accordingly, it is the privilege of a perfect man truly to recognize the Beloved. In reality, only holy men are the friends of God and friends to each other, but no one of the wicked or stupid is a friend. The beauty of friendship does not fall into a depraved state, since nothing shameful or incongruous can be capable of the harmonious union of friendship. Ask yourself these questions: Are you His friend? Or, are you only an acquaintance? Or, maybe even an enemy? How would you describe the intensity of your love for Him? Are you only a servant carrying out His commandments? To be His friend one needs to be ever changing with ever increasing love. He needs to be working on perfecting this friendship each and every day.
A friend of God is one who has "a steadfast and immovable love for Christ."
Reference: Saint Basil's Commentary on the Psalms, Homily 17