For nothing is hidden that will not be made manifest, nor is anything secret that will not be known and come to light.
There are many commandments in the Torah; some are of outwardly visible obedience, some are of a more internal nature. It is easy to pride ourselves with obedience by mostly concerning ourselves with the outwardly visible commands , the physical manifestations of obedience everybody can see. Everyone can see what we eat, sometimes. Everyone can hear the words we say, sometimes. Everyone can see our tzitzits, if we wear them outwardly. Not everyone can see and hear what goes on in the privacy of our homes, our bedrooms, even much less the things that go on in our hearts, or in our souls. Pride and self-righteousness are also difficult to detect in someone, and the last person to notice them in ourselves is us.
When the Children of Israel arrived near the Land, they were asked to climb up on two mountains and renew their covenant (contract) with Hashem. They were to conduct an elaborate ceremony pronouncing a carefully selected series of curses and blessings. Looking over the curses in this ceremony, it seems that they were concerning hidden sins; the things we do in private. In this ceremony, heaven and earth were called as witnesses as to how the children of Israel will live while in the Land (Deuteronomy 27: 11-26)..
Yeshua often rebuked religious folks for hypocrisy. He rebuked those who made a big outward show of religion at the cost of spiritual pride reflected in self-righteousness, prejudice, and intolerance.
As we search our hearts in this season preceding Yom Kippur, may we make sure to attend to our hidden sins. The wise King teaches us that iron sharpens iron (Proverbs 27:17), so if we cannot find the things we need to work on in our lives, we may engage the help of close friends, spouses, or teenage children. These people know us best. May we not resist the hard truth the Holy Spirit may inspire them to tell us. This is the only way to grow. God already knows these things about us; we are the ones who need to discover them. As we open our hearts to rebuke and correction, our Father who sees in secret will reward us (Matthew 6:18).