The most basic motivation that the Bible offers is the threat of punishment if we do not obey God; however, the wrath that awaits us is not an immediate punishment in this life. Though disobedient people face consequences in this life, the ultimate and final punishment will be executed on the last day – eternal separation from God in hell:
"… When the Lord Jesus is revealed from heaven with His mighty angels, in flaming fire taking vengeance on those who do not know God, and on those who do not obey the gospel of our Lord Jesus Christ. These shall be punished with everlasting destruction from the presence of the Lord and from the glory of His power" II Thessalonians 1:7-9 (see also Matthew 5:27-30; 10:28; 13:40-42; 25:41-46; Romans 2:5-9)
Not only does God motivate us through the fear of hell, He also encourages us through the promise of eternal rest in heaven with Him:
"Let not your heart be troubled; you believe in God, believe also in Me. "In My Father's house are many mansions; if it were not so, I would have told you. I go to prepare a place for you. And if I go and prepare a place for you, I will come again and receive you to Myself; that where I am, there you may be also." John 14:1-3 (see also Matthew 5:12; 25:31-40, 46; II Corinthians 5:1; Revelation 21:1-22:5)
It is because of these basic motivations that most people become Christians. However, as we mature, God provides other forms of motivation that should encourage us to do His will.
Sense of Duty
As we grow and learn more about God, His power, and His majesty, we begin to appreciate the debt that we owe Him as our Creator.
"God, who made the world and everything in it, since He is Lord of heaven and earth, does not dwell in temples made with hands. Nor is He worshiped with men's hands, as though He needed anything, since He gives to all life, breath, and all things. And He has made from one blood every nation of men to dwell on all the face of the earth, and has determined their preappointed times and the boundaries of their dwellings, so that they should seek the Lord, in the hope that they might grope for Him and find Him, though He is not far from each one of us." Acts 17:24-27
Since He has given us life, we owe Him our service, but more importantly, we should also feel indebted because He paid for our ruined souls with the sacrifice of Jesus upon the cross:
"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? For you were bought at a price; therefore glorify God in your body and in your spirit, which are God's." I Corinthians 6:19-20 (see also I Peter 1:15-19)
Therefore, we are obligated to God for giving us life twice. The first unrepayable debt is our creation, and the second is our opportunity for spiritual restoration through Jesus' blood.
The Noblest Motivation – Love
The responsibility that we may feel toward God is not the final motivation that a mature Christian should realize. Ultimately, Christians will grow to the point that they appreciate the love and sacrifice that God made for us through Jesus' death.
"For when we were still without strength, in due time Christ died for the ungodly. For scarcely for a righteous man will one die; yet perhaps for a good man someone would even dare to die. But God demonstrates His own love toward us, in that while we were still sinners, Christ died for us." Romans 5:6-8
"In this is love, not that we loved God, but that He loved us and sent His Son to be the propitiation for our sins. … We love Him because He first loved us." I John 4:10,19
As a Christian grows and becomes more like Jesus, our example, he or she will be motivated to obey God out of their love for God and for others. This is the noblest motivation.