In Numbers 15, we read of the Lord’s command concerning tassles:
37 The LORD said to Moses,38 “Speak to the people of Israel, and tell them to make tassels on the corners of their garments throughout their generations, and to put a cord of blue on the tassel of each corner.39 And it shall be a tassel for you to look at and remember all the commandments of the LORD, to do them, not to follow after your own heart and your own eyes, which you are inclined to whore after.40 So you shall remember and do all my commandments, and be holy to your God.41 I am the LORD your God, who brought you out of the land of Egypt to be your God: I am the LORD your God.”
The principle remains in the NT, yet the tassels have been replaced:
12 Take care, brothers, lest there be in any of you an evil, unbelieving heart, leading you to fall away from the living God. 13 But exhort one another every day, as long as it is called “today,” that none of you may be hardened by the deceitfulness of sin. 14 For we have come to share in Christ, if indeed we hold our original confidence firm to the end.
Hebrews 3:12-14. It is interesting to note that this command to exhort one-another comes in the context of warning against the hardness of heart of the people in the wilderness (quoting Psalm 95).
It is for this reason that failing to congregation is so dangerous and thus carries such a grave warning:
23 Let us hold fast the confession of our hope without wavering, for he who promised is faithful. 24 And let us consider how to stir up one another to love and good works, 25 not neglecting to meet together, as is the habit of some, but encouraging one another, and all the more as you see the Day drawing near. 26 For if we go on sinning deliberately after receiving the knowledge of the truth, there no longer remains a sacrifice for sins, 27 but a fearful expectation of judgment, and a fury of fire that will consume the adversaries.
Hebrews 10:23-27. Here is a central aspect of discipleship: Jesus has defined discipleship as teaching others to observe Jesus’ commands (Matthew 28:20, “teaching them to observe all that I have commanded you”). The OT command is to wear tassels to constantly remind oneself of the commands of God. In the New Covenant, the work pictured by the tassels becomes the command for the entire congregation: all of you exhort, encourage, provoke one another:
And let us consider how to stir up one another to love and good works,
Hebrews 10:24. This work is a core work of discipleship — and it is given to the entire congregation. This is the message of the NT, not just of Hebrews:
I myself am satisfied about you, my brothers, that you yourselves are full of goodness, filled with all knowledge and able to instruct one another.
By way of application, we must consider be filled with the Scriptures so that we have something to say — discipleship is teaching what Jesus has commanded, not what we have invented (Matt. 28:20). Second, the power of transformation is in the Scripture:
For whatever was written in former days was written for our instruction, that through endurance and through the encouragement of the Scriptures we might have hope.
Romans 15:4. Third, we must realize that we each have this obligation to exhort one-another, it is not merely the duty of some pastor or overseer. Fourth, we must pray for the wisdom and grace to perform this work. Fifth, we must repent of failure to do so, whether for laziness or a failure of love. Sixth, we must do the work.