Gal 3:24 Wherefore the law was our schoolmaster [to bring us] unto Christ, that we might be justified by faith.
In the above scripture how the Law profits one (the unbeliever and self-righteous) is clearly stated. In this discourse, I would highlight some methods by which the schoolmaster achieves this purpose.
The Law in itself is Perfect. Perfect in purpose and methods of execution. We sometimes find ourselves in the shoes of the Pharisee who went to pray with the Publican in Luke 18:9-14. We look at how consistent we have been in the discharge of our Christian duties and either a conscious or subconscious sense of righteousness due to what we have been able to do gives us the assurance that we are saved. We say "By the Grace of God" but deep within us, we trust in our own merits. Like that Pharisee, we perceive that we are "more saved" than another fellow in Church.
Some of us get into this state due to probably a great zeal to maintain a Godly standard in our society to the extent that our attitude presents to people that we are saved by those things. This can be evidence that we have not encountered the Salvation through Faith. I am sure God then sends the schoolmaster in full force to direct us to Faith in Only Jesus Christ. The Law comes to tell you that if you have not obeyed EVEN ONE of my commands then you are guilty of all and of Sin and its full wages i.e DEATH.
To some self-righteous people, the Law places itself side-by-side with what you see as your Best Work (which makes you think you are accepted by God) and you start getting a clear picture of your Sinfulness and unworthiness. The Law, like the rod of Moses, turns into a huge Snake and swallows up your tiny snakes of self-righteous deeds. The Law again like Shylock in Shakespeare's Merchant of Vernice, fully demands "its pound of flesh" from anyone that falls short of it.
You start to feel so helpless and you are driven to seek help. The Law is able to give you a Perfect Diagnosis BUT NOT THE CURE. By the Law, you are thrust into the State of NOTHINGNESS in your own self. You are finally broken down and driven to the feet of the Cross. You find yourself kneeling at the feet of Cross and like the Publican, you feel so shameful to even raise up your eyes to Christ.
A picture of the Purchase by Christ's Blood is shown to you and the scenes of the Cross become very real to you. From there you realize that you are forgiven many therefore you are moved to love many. Your prayer now becomes, "God be merciful unto me a sinner". You are then appreciate that you are Justified by Faith in Jesus Christ and His Righteousness is imputed unto you.
Surely you have attained unto the Blessed Assurance. Through the Holy Spirit, all the good works gradually become manifest in you for God's good pleasure making you bear Fruits to His Glory. You realize that the Law has therefore served its purpose.
Any sense/feeling of being "more saved" which stems from how good we have discharged our Christian duties is like the intermittent glow of a bulb that shows the dimming of one's light. It is a great indication of the working of Self-righteousness within a person.
These are scriptures that are able to put us back on track to eliminate the tiny traces of self-righteousness:
Isa 64:6 But we are all as an unclean [thing], and all our righteousnesses [are] as filthy rags; and we all do fade as a leaf; and our iniquities, like the wind, have taken us away.
1Co 4:7 For who maketh thee to differ [from another]? and what hast thou that thou didst not receive? now if thou didst receive [it], why dost thou glory, as if thou hadst not received [it]?
Luk 17:10 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.
I would conclude with Gal 3:25 "But after that faith is come, we are no longer under a schoolmaster". Glory to God that we are no longer under the Law. Continue in the Grace of God by Faith in Jesus Christ. Our salvation hinges on what has been done ONCE by JESUS CHRIST on the Cross for us and NOT by WHAT WE ARE ABLE TO DO DAILY before or after we are saved.