All believers should abide by Peter's exhortation and give earnest diligence toward the development of spiritual qualities:
According as his divine power hath given unto us all things that pertain unto life and godliness, through the knowledge of him that hath called us to glory and virtue:
Whereby are given unto us exceeding great and precious promises: that by these ye might be partakers of the divine nature, having escaped the corruption that is in the world through lust. And beside this, giving all diligence, add to your faith virtue; and to virtue knowledge; And to knowledge temperance; and to temperance patience; and to patience godliness; And to godliness brotherly kindness; and to brotherly kindness charity. For if these things be in you, and abound, they make you that ye shall neither be barren nor unfruitful in the knowledge of our Lord Jesus Christ. But he that lacketh these things is blind, and cannot see afar off, and hath forgotten that he was purged from his old sins. Wherefore the rather, brethren, give diligence to make your calling and election sure: for if ye do these things, ye shall never fall: For so an entrance shall be ministered unto you abundantly into the everlasting kingdom of our Lord and Saviour Jesus Christ. - 2 Peter 1:3-11
It is important to note (if one digs a little into definitions) that most, if not all, of these can be included amongst the list of fruits of the spirit:
But the fruit of the Spirit is love, joy, peace, longsuffering, gentleness, goodness, faith, Meekness, temperance: against such there is no law. - Galatians 5:22-23
This means that we are to give diligence towards the exercise of abilities or the fulfillment of capacities that have been given to us rather than addition to ourselves merely by ourselves. As the Apostle Paul often likes to say, we must walk in and mind these things rather than fleshly things.
But now, how are we to regard these things? How are they to be perceived and considered in ourselves and others? Jesus said that whoever would be great among us, let him be the servant of all. This is a good baseline for self judgement as it hits motivation as well as activity. Do I serve others so that I will be seen as great? That is probably an epic fail:
So likewise ye, when ye shall have done all those things which are commanded you, say, We are unprofitable servants: we have done that which was our duty to do. - Luke 17:17
We are to examine ourselves daily to see whether we are in the faith. This is sort of like a touchstone in the list from 2 Peter. All of these things that we are to add are to be added to our faith and we should daily (read that as constantly) be attentive that our spiritual progress remains vitally connected back to our faith. This entire process should be overlayed and underpinned by a confidence, not in ourselves, nor in any religious superstructure, but in God Himself...Christ in us, the hope of glory. Do I have such faith that God can bring about spiritual progress in my life that I earnestly seek to cooperate with this work?
Wherefore, my beloved, as ye have always obeyed, not as in my presence only, but now much more in my absence, work out your own salvation with fear and trembling. For it is God which worketh in you both to will and to do of his good pleasure. - Philippians 2:12-13
The estimation of spiritual progress in others is to follow self-estimation and to be laden with grace for we do not perceive the intent of another's heart. I must be willing to present my life honestly before others so that my self-estimation of my progress may be estimated by others and I may be encouraged or corrected:
Judge not, that ye be not judged. For with what judgment ye judge, ye shall be judged: and with what measure ye mete, it shall be measured to you again. And why beholdest thou the mote that is in thy brother's eye, but considerest not the beam that is in thine own eye? Or how wilt thou say to thy brother, Let me pull out the mote out of thine eye; and, behold, a beam is in thine own eye? Thou hypocrite, first cast out the beam out of thine own eye; and then shalt thou see clearly to cast out the mote out of thy brother's eye. - Matthew 7:1-5
There is a strong necessity for regular fellowship with the brethren so that we may all participate in exhortation, encouragement, rebuke, correction, etc. As it is written, "Iron sharpens iron" but only as the one rubs against the other. It is in regular Christian fellowship that attributes of spiritual maturity are evidenced:
This is a true saying, If a man desire the office of a bishop, he desireth a good work. A bishop then must be blameless, the husband of one wife, vigilant, sober, of good behaviour, given to hospitality, apt to teach; Not given to wine, no striker, not greedy of filthy lucre; but patient, not a brawler, not covetous; One that ruleth well his own house, having his children in subjection with all gravity; (For if a man know not how to rule his own house, how shall he take care of the church of God?) Not a novice, lest being lifted up with pride he fall into the condemnation of the devil. Moreover he must have a good report of them which are without; lest he fall into reproach and the snare of the devil. Likewise must the deacons be grave, not doubletongued, not given to much wine, not greedy of filthy lucre; Holding the mystery of the faith in a pure conscience. And let these also first be proved; then let them use the office of a deacon, being found blameless. Even so must their wives be grave, not slanderers, sober, faithful in all things. Let the deacons be the husbands of one wife, ruling their children and their own houses well. For they that have used the office of a deacon well purchase to themselves a good degree, and great boldness in the faith which is in Christ Jesus. - 1 Timothy 3:1-13
It is in the trials and temptations of life, of family, of work, and of Christian fellowship in the midst of a fallen world that the gold of spiritual progress is refined and shows forth. A church leader with an unruly household (or no household at all) how can they take care of the Church (asks Paul)? Someone who merely checks off the attend church box once a week, how can they be sharpened?
Whatever one does without love is worthless (1 Corinthians 13). The question is, do I trust the Lord Jesus Christ enough (He who works in me and in my brethren) do I trust Him enough in the process of my sanctification to completely expose my life to my brethren that they might perceive my condition and help me to grow? This is certainly the only way that I may help them, so then I must love them enough to be willing to expose myself to them.
Having therefore, brethren, boldness to enter into the holiest by the blood of Jesus, By a new and living way, which he hath consecrated for us, through the veil, that is to say, his flesh; And having an high priest over the house of God; Let us draw near with a true heart in full assurance of faith, having our hearts sprinkled from an evil conscience, and our bodies washed with pure water. Let us hold fast the profession of our faith without wavering; (for he is faithful that promised;) And let us consider one another to provoke unto love and to good works: Not forsaking the assembling of ourselves together, as the manner of some is; but exhorting one another: and so much the more, as ye see the day approaching. - Hebrews 10:19-25