Love: 

This includes first a love for God, then an accompanying love for others (Matt. 22:37-39).

 A Christian motivated by love works for the benefit of the One loved. Love for God is often demonstrated through obedience (John 14:21; 1 John 5:2). 

Love also expresses itself in a desire to glorify (John 12:27-28), please (Col. 1:10; 3:20; 1 Thes. 4:1), and know God (Phil. 3:10-14; 1 John 4:16).

 Love for God would also mean love for that which God loves, thus we love other people (2 Cor. 5:14; 12:15; 1 John 4:11; 5:2).

Gratitude:

 Because we benefit from God's actions, we may wish to respond gratefully. 

Our service and our lives become a "Thank You" to Him. In light of God's blessings, we are motivated to offer our bodies to Him (Rom. 12:1-2) and to live for Him (Gal. 2:20). 

Paul was motivated to serve God with thanksgiving (1 Tim. 1:12)

Eternal Significance: 

We can be motivated to fulfill our longing for some significance beyond this temporary life according to God's original purposes.

 God created us to participate in His rule over the earth (Gen. 1:26-28). 

This will be fulfilled in His coming kingdom to the degree that we are faithful in our responsibilities in this life (Matt. 19:27-30; Luke 19:11-27) or our faithful endurance in suffering (Rom. 8:17; 2 Tim. 2:12).

 The enjoyment of this earned inheritance should inspire godly conduct (1 Cor. 6:9-11; Gal. 5:21; Eph. 5:5).

The book of Hebrews promises those who are faithful a share in Christ's future rule (Heb. 1:14; 3:14; 4:1, 9; 6:11-12). 

Eternal significance can begin when we engage in serving Christ in this life (Matt. 10:38-39; 16:24-27; Luke 9:23-26).

Rewards: 

We can also be motivated by God-given rewards in this life (Mark 10:28-31) and in eternity (Matt. 16:27; Rev. 22:12).

 The judgment seat of Christ is the scene of future rewards.

 There all Christians will appear and give an account (Rom. 14:10-12; 2 Cor. 5:10; 1 Cor. 3:9-13). 

Eternal rewards include treasures (Matt. 6:20) and crowns (1 Cor. 9:25; 1 Pet. 5:4; 2 Tim. 4:8).

 Motivation also comes from the possibility of losing out on eternal rewards (Matt. 22:1-14; 25:14- 25; Luke 19:11-27; 1 Cor. 3:12-15).

 Rewards are not a selfish motivation if our goal is to use them to glorify God in the end.

Duty: 

Some Christians will serve God because they have made a commitment to do so, or because they are living up to that which God has called them to do.

 Duty does not expect a reward, but is performed out of obligation (Luke 17:7-10).

 This is seen in Jesus' own commitment to do what God had called Him to do (Mark 1:38; John 12:27; 17:4; Heb. 2:17; 5:5-10).

 Paul was motivated to live up to his calling to be an apostle to the Gentiles (Acts 20:24; 2 Tim. 1:1, 11; 2:7).

 Christians might also feel it their duty to be faithful stewards of their gifts (Rom. 12:6-8; 1 Tim. 4:14; 1 Pet. 4:10-11) or the gospel (1 Cor. 9:17-18; Col. 1:25; 1 Tim. 1:11, 18; 6:20; 2 Tim. 2:14; 2:2; Titus 1:3).

Fear: 

This motivation is inferior to love (1 John 4:18) but can motivate the Christian away from sin or unfaithfulness and towards godly conduct.

 One might fear a negative judgment at the judgment seat of Christ (James 2:13; 3:1) which can include shame (2 Tim. 2:15; 1 John 2:28) or loss of reward (1 Cor. 3:13-15; 9:27).

 The Christian may also fear God's temporal discipline (1 Cor. 5:5; 11:29-32; Col. 3:23-25; 1 Tim. 4:14; James 5:15-16, 19).

 The book of Hebrews effectively uses five fearful warnings to motivate its readers away from apostasy and on to maturity (Heb. 2:1-4; 3:7 - 4:13; 6:1-12; 10:26-31; 12:25-29). 

There is also a positive aspect of fear in the sense of reverence, which is also a motivation for the Christian (Acts 10:2; 2 Cor. 7:1; Eph. 5:21; Phil. 2:12; Heb. 12:28