Hebrews 3:12-15 meaning

The Pauline Author continues his warning; he wants believers to avoid an evil, unbelieving heart, like the hearts that the Israelites demonstrated when they were too afraid to confront and take possession of the Promised Land. He writes: Take care, brethren, that there not be in any one of you an evil, unbelieving heart that falls away from the living God (v 12). 

The next chapter will assert that the people heard God, but it provided them no benefit because they did not believe and act upon what they heard (Hebrews 4:2). They had an unbelieving heart. 

The phrase fall away means to rebel against God's command. The Pauline Author is using the example of the Israelites' rebellion against God when they chose not to trust God and enter the Promised Land (Numbers 14:9). This illustration is given as a warning to his audience to not rebel against the living God. To hear and not act is described as stemming from an evil, unbelieving heart. This would be a heart bent on pride, following our own way, rather than faith, following God's way.

The Pauline Author offers some instruction on how to avoid turning away from the living God—But encourage one another day after day, as long as it is still called "Today," so that none of you will be hardened by the deceitfulness of sin (v 13). In other words, believers ought to encourage one another to be obedient to and trust God right now. To encourage one another to remain faithful and act on God's promises is the same basic idea asserted in Chapter 10:

"...and let us consider how to stimulate one another to love and good deeds, not forsaking our own assembling together, as is the habit of some, but encouraging one another; and all the more as you see the day drawing near."
(Hebrews 10:24-25)

Each person is accountable directly to God for their choices. But scripture directs us to encourage and support one another to follow God's ways rather than follow in the deceitfulness of sin. Sin promises a lie, which is that we will gain the most life and benefit from following our own way. The truth is that there are only two paths, slavery to sin and slavery to righteousness (Romans 6:16). Walking in righteousness (alignment with God's design to love and serve others) is the path that leads to our greatest benefit.

Like physical birth, being born again is a one-time event (John 3:3, 14-15). But walking by faith occurs day after day. And the only day we can make choices and take actions is Today. Like the first generation of Israel that came out of Egypt, our opportunity to make good choices can pass, so we are exhorted to grab the opportunity when we have it. That time is now.

"Now" is the only time we can take any action; we can only put our faith into practice in the present. Today emphasizes the urgency of encouragement and obedience; the past has already happened and the future is always in front of us, but today we have an opportunity to turn to God in obedience. 

Each day we fail to walk in faith is a day we risk being hardened by the deceitfulness of sin. Like the first generation, this can lead us to lose the reward of our inheritance. Anytime we decline to follow God, we are heading down the path of being hardened, of being deceived that the world's ways (which actually lead to death) will lead us to life. 

Earlier, the Pauline Author said that we as believers could be a part of God's ruling household based on our obedience. Here the Pauline Author says that we have become partakers of Christ, if we hold fast the beginning of our assurance firm until the end (v 14). The word partakers is "metochos" in the Greek which can also be translated companion, referencing the believer's journey with Christ in walking toward maturity. 

"Metochos" is used throughout (Hebrews 3:1, 3:14, 6:4). It means to be a participator, a sharer, or a business partner. We share in Christ's reward if we live our life in faithful obedience, walking in communion with Him. Hebrews exhorts believers to partake in Christ's life by learning obedience even as He learned, following His Father's will even unto death (Philippians 2:8). This is done by living the resurrection life of Jesus by faith in our everyday lives.

Companionship refers to the fellowship we have with Jesus as we live our lives in obedience to God and in harmony with others. We are companions, partakers, and co-heirs with Christ if we hold fast until the end of our lives on this earth (Revelation 3:21). Jesus desires to bring many sons to glory (Hebrews 2:10). In this case a "son" is someone that received the reward of reigning. This is a similar reward of "Son" that Jesus is depicted as receiving in Chapter 1 (Hebrews 1:5, 8, 13). 

The assurance referred to is the confidence that God's rewards will be more than worth the loss and suffering that comes from being rejected by the world (Hebrews 11:6, 12:1-2). This repeats the same basic idea as in Hebrews 3:6, where we are said to be a "son" if we "hold fast our confidence and the boast of our hope firm until the end." The emphasis is to complete the task of living in faith until our lives are done. 

The Pauline Author repeats a portion of the quote from Psalms 95:7-11 as a warning conveying his sense of urgency: While it is said, "Today if you hear His voice, do not harden your hearts, as when they provoked Me" (v 15). Today, while we have the opportunity, let us obey God. We cannot walk in fellowship/companionship with God in this life with a hardened heart of disobedience, and we cannot enjoy the amazing inheritance God has set aside for us if we do not possess it through a walk of faith.

The reference to as when they provoked Me refers to the first generation of Israel that came out of Egypt who disobeyed God. They saw God's provision in leading them out of Egypt, parting the sea, and leading them with a cloud by day and a fire by night. (Exodus 13:21, 14:21). But they did not persevere in faith, and refused to enter the land. Therefore God did not allow that generation to possess their inheritance (Numbers 14:21-23). The believers are exhorted to not make that same mistake.

We will see in Hebrews 10:32-35 that the recipients of this letter have already walked a life of faith to this point. They are being exhorted not to falter, to continue on in spite of difficulty. To keep looking at and having confidence in Christ and His reward rather than being distracted by religious observance.