Romans 15:4-6 meaning

Paul has effectively and frequently used the Old Testament to validate his teachings, as he just did in the previous verse referring to Psalm 69. There he spoke of Jesus's willingness to endure the reproach of others in obedience to His Father. 

Here Paul explains one reason why the Old Testament was written and why these ancient texts were preserved: to give us hope: For whatever was written in earlier times was written for our instruction, so that through perseverance and the encouragement of the Scriptures we might have hope (v 4). 

Hope comes from being instructed, persevering, and being encouraged by the Scriptures, such as Psalm 69, that point us to Jesus's example. Jesus endured rejection from the world in order to please His Father, and in doing so gained His Father's joy, which was the greatest of rewards (Hebrews 12:1-2). The Father greatly exalted His Son because of His obedience (Philippians 2:8-9; Hebrews 1:5, 8, 13, 2:9-10; Revelation 3:21; Matthew 28:18). Jesus entered in to the joy of His Master, and so taught His disciples to follow Him (Matthew 25:21). 

By these examples we are taught and spurred on to be confident, putting our hope in God's promise that our obedience will actually lead us to the greatest of rewards. We are also given great examples of believers who trusted God in their lives and cared for one another. They are elevated in scripture as being great in God's sight. Figures like Abraham and Noah are highlighted in Hebrews 11 as being examples of faith. 

Paul asks that God also give the readers of this letter a unified mind with each other, founded on Christ Jesus: Now may the God who gives perseverance and encouragement grant you to be of the same mind with one another according to Christ Jesus (v 5).

The Greek word "phroneo" is translated the same mind. Paul uses "phroneo" as the primary theme of his letter to the Philippians. He exhorts the Philippians to have the same "attitude" ("phroneo") as Jesus chose when He decided to follow His Father's will to take on human form and die on the cross (Philippians 2:5-9). A mind or attitude is a perspective that is chosen. It is inferred here that choosing the right perspective is a vitally important choice we make—a choice that shapes our actions. 

The "phroneo" or attitude/mindset Paul exhorts us to choose is not the same mind according to the world and its ways, but the same mind that is according to Christ Jesus. The attitude or mindset that Jesus chose was to look at the "joy set before Him" and willingly endure the cross (Hebrews 12:2). Jesus had the hope of pleasing His Father by following His ways, and that hope caused Him to choose to walk in service to the world (John 3:16). 

In being united in their mindset, Paul says with one accord you may with one voice glorify the God and Father of our Lord Jesus Christ (v 6). When we live in harmony with other believers, we are enabled to glorify God. The Greek word translated glorify is the verb form of "doxa" (glory). Glory is simply something's essence being observed by others. When we walk with one accord, being like minded, it is then that we are showing the essence of God. We are therefore showing God to others through our actions of living in harmony with one another. 

When we have such harmony, we speak as with one voice and show the nature of our creator. God created the world to be in harmony. He placed humans over the earth to reign in dominion, and to reign in harmony with Himself and one another. Scripture calls this assignment to reign over the earth "glory and honor" (Hebrews 2:5-7). 

But the world fell into disharmony through the Fall of Man, through humans choosing our own way instead of following God's way (Genesis 3:6). The current earth is, therefore, not functioning as it was designed. But Jesus has restored the glory of humanity reigning over the earth. He did so through the "suffering of death" (Hebrews 2:9). He invites all believers to follow His example (Hebrews 2:10). It is through laying down self that we restore God's (good) design for the world, and bring glory to Him.

God created us to live at peace with one another. Believers are made to be unified through the Scriptures, which give us hope, encouragement, and instruction. With this unification, we as believers should with one voice glorify the God and Father of our Lord Jesus Christ.

God of course does not need us in order to be glorified. "Glory" in Scripture is used to describe an observed object having its true essence shine forth to the observers. For example, in Paul's first letter to the Corinthians, he mentions that the sun, earth, and moon each have "glory," but their glory differs because their essence differs (1 Corinthians 15:40-41). 

The heavens and all of creation continually declare the glory of God because all that is made reflects His image (Psalm 19). The amazing opportunity believers enjoy is to display the essence of God—we can do this by showing God's love toward us to others in our daily lives, thus copying Jesus's example. When we abide in Christ and live according to His ways, we glorify the Father (John 15:7-8).

When we serve as Jesus serves, we have the hope of pleasing God as Jesus pleased God (Philippians 2:9; 1 Peter 5:6). Jesus even gives believers the stunning promise that if we overcome as He overcame, He will share His reward with us (Revelation 3:21).