“Behold, how good and how pleasant it is 
 For brethren to dwell together in unity!”  Psalm 133:1
(In my NKJV study Bible Psalm 133 is entitled “Beauty of the Unity in the Brethren”)

Unity!  Our Scripture lets us know that it is the unity of believers.  What is this unity based upon?  

It is based upon:
The indwelling Spirit:
“Do you not know that you are the temple of God and that the Spirit of God dwells in you?”  1 Corinthians 3:16
Also in 1Corinthians 6:19,
“ Or do you not know that your body is the temple of the Holy Spirit who is in you, whom you have from God, and you are not your own?”

New birth:
“Therefore, if anyone is in Christ, he is a new creation; old things have passed away; behold, all things have become new.”  2 Corinthians 5:17

Union with Christ:
In 2 Corinthians 13:5 we are told to,
“Examine yourselves as to whether you are of the faith.  Prove yourselves.  Do you not know yourselves, that Jesus Christ is in you?”
(For assurance read Romans 8:31-39 and rejoice!)

Unity is expressed--
By oneness of mind:
“...all of you be of one mind, having compassion on one another; love as brothers, be tenderhearted, be courteous.”  1 Peter 3:8

 By faith:
“There is one body and one Spirit, just as you were called in one hope of your calling; 
One Lord, one faith, one baptism;
One God and Father of all, who is above all, and through all and  in you all.”   
Ephesians 4:4-6
(Read Vs. 1-11 of this chapter for it gives an exhortation to unity, an explanation of unity, the means for unity--the gifts.)

Unity is expressed in concern for one another:
“There should be no schism (division) in the body, but that the members should have the same care for one another.
And if one member suffers, all the members suffer with it; or if one member is honored all the members rejoice with it.”  1 Corinthian 12:25-26
Read these verses in context for a full meaning of the text.  In fact please read ALL the verses in context for the full meaning of each.

Unity is expressed in fellowship:
There are many verses in Scripture that speak of Christian fellowship.
One example is the fellowship of believers in the practices of the early church.  
Read Acts 2:42-47.
Vs. 42 tells us,
“And they continued steadfastly in the apostles’ doctrine and fellowship, in the breaking of bread, and in prayer.”

I close with Psalm 133:

“Behold, how good and how pleasant it is
 For brethren to dwell together in unity!
 
 It is like the precious oil upon the head,
 Running down on the beard,
 The beard of Aaron,
 Running down on the edge of his garments.

 It is like the dew of Hermon,
 Descending upon the mountains of Zion;
 For there the LORD commanded the blessing--
 Life forever more.

Thank you most holy God for life forevermore, in Christ Jesus our Lord and Savior.  Amen