The main ideas here are taken from the book ‘Reflections of a Discerning Christian’ by Nelson Thomas.  I have also added a few of my own points after meditating on the same verses.
Discernment is defined as the ability to evaluate and judge a situation and understand that which is not obvious.  In this post, we will explore what discernment means in Christian life.

1. It is a privilege of a born-again believer only

• 1 Corinthians 2:14,15 - But the natural man does not receive the things of the Spirit of God, for they are foolishness to him; nor can he know them, because they are spiritually discerned. But he who is spiritual judges all things, yet he himself is rightly judged by no one.

• The natural man is the unsaved man.  Spiritual things seem foolish to the natural man and he doesn’t want them.  He also cannot understand them, because he doesn’t have that spiritual discernment.  

• Psalm 92:6 - A senseless man does not know, Nor does a fool understand this.

• When looking at this verse, you must have the context of the rest of the chapter - Psalm 92.  The senseless man doesn’t understand God’s greatness or the coming judgment.  This senseless man doesn’t have the privilege of discernment.

• A child of God, by virtue of the indwelling Holy Spirit, has the capability to discern and take right decisions in spiritual life. 

• A true believer in Christ has the resources by which they can differentiate between good and bad

2. We need to progress in the ability of discernment

• Philippians 1:9 - And this I pray, that your love may abound still more and more in knowledge and all discernment,

• Paul specifically calls out to the Philippian church that not only should they abound more in love, but also in knowledge and discernment.  They should not have blind love.  They should also have discernment to love the things that God approves and being excellent.

• As we progress in our Christian lives, we ought to improve in our ability to distinguish between what is right and wrong

• As the days go by, we must become more and more sensitive to the will of God

3. Discernment in spiritual matters proves the maturity of our Christian life

• Hebrews 5:14 - But solid food belongs to those who are of full age, that is, those who by reason of use have their senses exercised to discern both good and evil.

• The idea here is that solid food is for those who are more mature.  It should be part of the diet of a believer.  Our senses can be trained to discern between good and evil, both from a doctrine and a moral perspective.  

• 1 Corinthians 3:1-3 - And I, brethren, could not speak to you as to spiritual people but as to carnal, as to babes in Christ. I fed you with milk and not with solid food; for until now you were not able to receive it, and even now you are still not able; for you are still carnal. For where there are envy, strife, and divisions among you, are you not carnal and behaving like mere men?

• The people mentioned here are part of God’s family.  They are believers, they have the Holy Spirit, but they are not behaving like spiritual people.  Paul has 3 categories of people.  The natural man is the one in 1 Corinthians 2 (mentioned earlier) who rejects the things of God.  The spiritual man knows and accepts the things of God.  The carnal man knows the things of God, but is still living a worldly life. 

• In the Corinthian church, they were still babes in Christ, not able to digest solid food.  This shows their spiritual immaturity.  Even though they thought they were spiritual, the divisions among themselves showed that they were carnal.  They were not behaving in a spiritual manner.

• Immature and childish Christians are called carnal.  Maturity means having the right perspective.

4. There are specific areas where discernment is indispensable

• The Word of God specifically mentions certain areas where discernment is a must

• Regarding what is good and evil

• Hebrews 5:14 - But solid food belongs to those who are of full age, that is, those who by reason of use have their senses exercised to discern both good and evil.

• Refer to point # 3. 

• 1 Thessalonians 5:21 - Test all things; hold fast what is good.

• Evil and deception can be present even in a spiritual setting, so believers are tasked with testing everything.  The test is not against our own morality, but according to the standard that is God and His Word, as well as the discernment given to us by the Spirit.  Once we know if something is good, we have to hold fast to it.  

• Regarding what is holy and unholy and what is clean and unclean

• Leviticus 10:10 - that you may distinguish between holy and unholy, and between unclean and clean

• This is the first of the priestly responsibilities given to Aaron and his sons.  They had to be able to discern and explain the difference between holy and unholy, as well as what is clean and unclean.  

• Regarding what is acceptable and unacceptable

• Ephesians 5:10 - finding out what is acceptable to the Lord.

• Before becoming a believer, we were in darkness.  But after coming to Christ, we are in the light and we must walk as such.  With the Holy Spirit indwelling in us, we should have goodness, righteousness, and truth in our lives.  By walking in this way, we can find out what is acceptable to God.

• Regarding what is true and false

• 1 John 4:1 - Beloved, do not believe every spirit, but test the spirits, whether they are of God; because many false prophets have gone out into the world.

• John advises not to assume that every spiritual experience or demonstration of power comes from God.  As believers, we need to test them to see if they are from God.  There are many false prophets with false messages in the world and it is a believer’s responsibility to discern between the truth and the lies.

• Regarding what is excellent and poor

• Philippians 1:10 -  that you may approve the things that are excellent, that you may be sincere and without offense till the day of Christ,

• When we approve and receive the things that are excellent, we become more righteous.  This is not a one-time thing.  We should continue in this manner and have it evident in our lives until Christ comes back.  

• Only a Spirit-filled and mature person makes such a high level of spiritual discernment.

5. God takes discernment very seriously

• Ezekiel 22:26 - Her priests have violated My law and profaned My holy things; they have not distinguished between the holy and unholy, nor have they made known the difference between the unclean and the clean; and they have hidden their eyes from My Sabbaths, so that I am profaned among them

• God has a set standard and we are separated and called to be His own special people that follow that standard.

6. Poor discernment could be a part of divine judgment 

• Isaiah 44:18 - They do not know nor understand; For He has shut their eyes, so that they cannot see, And their hearts, so that they cannot understand.

• This portion is referring to idol makers who should very obviously see the error of their ways.  But God has shut their eyes and hearts.  The people first chose to be in darkness and were willfully blind.  After some time, God gave them up to do what they wanted.  Their discernment was lost.