We must take care not to refer all the merits of the saints to the Lord in such a way as to ascribe nothing but what is evil and perverse to human nature, in doing which we are confuted by the evidence of the most wise Solomon, or rather of the Lord himself, whose words these are; for when the building of the temple was finished and he was praying, he spoke as follows: ‘and David my father would have built a house to the name of the Lord God of Israel: and the Lord said to David my father: Whereas thou hast thought in thine heart to build a house to my name, thou hast done well in having this same thing in thy mind.’ This thought and purpose of King David, are we to call it good and from God or bad and from man? For if the thought was good and from God, why did He by whom it was inspired refuse that it should be carried into effect? But if it is bad and from man, why is it praised by the Lord?

St. John Cassian

Not every "good" deed is actually good, but only that good deed which is done for the sake of God.  The externals of a particular action are not its essence; God alone sees a person's heart.  We need to humble ourselves, realizing that every good deed is mixed with some passion.

St. Nikon of Optina

A Christian must be courteous to all. His words and deeds should breathe with the grace of the Holy Spirit, which abides in his soul, so that in this way he might glorify the name of God. He who regulates all of his speech also regulates all of his actions. He who keeps watch over the words he is about say also keeps watch over the deeds he intends to do, and he never goes out of the bounds good and benevolent conduct. The graceful speech of a Christian is characterized by delicateness and politeness. This fact, born of love, produces peace and joy. On the other hand, boorishness gives birth to hatred, enmity, affliction, competitiveness, disorder and wars.

St. Nectarios of Aegina

Virtue does not consist in many different visible bodily activities, but in a heart that is wise in what it hopes for, and whose actions are accompanied by a right intention.

St Isaac of Syria