In pondering the expression “let us” I came across Jeremiah 9:23-24 which speaks of ‘let not‘.
“Thus says the LORD:
‘Let not the wise man glory in his wisdom, 
Let not the mighty man glory in his might, 
Nor let the rich man glory in his riches,
But let him who glories glory in this,
That he understands and knows Me,
That I am the LORD exercising loving-kindness  
    judgment, and righteousness in the earth.
For in these I delight,’ says the LORD.”
 
Now, let’s see what the ‘let us’ Scriptures have to tell us.
Jesus speaking to His disciples,
“But that the world may know that I love the Father, and as the Father gave Me commandment, so I do.  Arise, ‘let us’ go from here.”  John 14:31
 
In Romans 13:12-13,
“The night is far spent, the day is at hand.  Therefore ‘let us’ cast off the works of darkness, and ‘let us’ put on the armor of light.  ‘Let us’ walk properly, as in the day, not in revelry and drunkenness, not in licentiousness and lewdness, not in strife and envy.”
Vs. 14 goes on to say,
“But put on the Lord Jesus Christ, and make no provision for the flesh, to fulfill its lusts.”
 
“But ‘let us’ who are of the day be sober, putting on the breastplate of faith and love, and as a helmet the hope of salvation.”  1 Thessalonians 5:8
 
The ‘let us’ in Hebrews are many as we see in the following and please note in each verse is the word ‘therefore’ in your personal study go back to see what the writer of Hebrews is referring to:
 
Hebrews 4:1,
“Therefore, since a promise remains of entering His rest, ‘let us’ fear lest any of you seem to have come short of it.”
 
“‘Let us’ therefore be diligent to enter that rest, lest anyone fall after the same example of disobedience.”  Hebrews 4:11
 
“‘Let us’ therefore come boldly to the throne of grace, that we may obtain mercy and find grace to help in time of need.”  Hebrews 4:16
 
Hebrews 6:1 speaks of going on to maturity,
“Therefore, leaving the discussion of the elementary principles of Christ, ‘let us’ go on to perfection (maturity), not laying again the foundation of repentance from dead works and of faith toward God.”
 
Hebrews 10:22, 23, 24 says draw near, hold fast, consider one another:
“‘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 confession of our hope without wavering, for He who promised is faithful.
And ‘let us’ consider one another in order to stir up love and good works,”
Vs. 24 goes on to say,
“not forsaking the assembling of ourselves together, as is the manner of some, but exhorting one another, and so much the more as you see the Day approaching.”
 
“Therefore we also, since we are surrounded by so great a cloud of witnesses, ‘let us’ lay aside every weight, and the sin which so easily ensnares us, ‘let us’ run with endurance the race that is set before us.”  Hebrews 12:1
 
Hebrews 13:13,
“Therefore ‘let us’ go forth to Him, outside the camp, bearing His reproach.”
And Vs. 15,
“Therefore by Him ‘let us’ continually offer the sacrifice of praise to God, that is, the fruit of our lips, giving thanks to His Name.”
 
Our desire is to know God’s ways.  Scripture tells us in 2 Timothy 3:16-17,
“All Scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness, that the man of God may be complete, thoroughly equipped for every good work.”
 
So with this in mind, we heed the ‘let us’ Scriptures as they are equipping each of us to do those good works that were created in which each Believer is to walk.
“For we are His workmanship, created in Christ Jesus for good works, which God prepared beforehand that we should walk in them.”  Ephesians  2:10
 
Thank you Holy God for loving us beyond measure!  Thank you for Your Word!  We worship You, adore You and give You all the glory.  Amen