"For the love of Christ constraineth us; because we thus judge, that if one died for all, then were all dead: And that he died for all, that they which live should not henceforth live unto themselves, but unto him which died for them, and rose again." (2 Corinthians 5:14-15)
There are many motivating reasons for serving the Lord. One, of course, is His many merciful blessings on our behalf. "I beseech you therefore, brethren, by the mercies of God, that ye present your bodies a living sacrifice, holy, acceptable unto God, which is your reasonable service" (Romans 12:1).
Then there is the incentive of rewards: "And, behold, I come quickly; and my reward is with me, to give every man according as his work shall be" (Revelation 22:12). There are also many rewards even in this present life for dedicated Christian service: "Godliness is profitable unto all things, having promise of the life that now is, and of that which is to come" (1 Timothy 4:8).
The great need of the lost is also a tremendous motivation for Christian service. This was the burden of Paul: "For though I be free from all men, yet have I made myself servant unto all, that I might gain the more" (1 Corinthians 9:19).
But surely the greatest of all motives is the constraining love of Christ. Not our love for Him, which is poor and weak at best, but His love for us. This is the constraining compulsion which makes us live and love and witness for Him. Because He loved us so much, therefore we no longer live for ourselves, but unto Him, who died for us.
As our text notes, if Christ died for all, that can only mean that "all were dead," or more literally, "all died." Therefore, if we live, it is because we have been "bought with a price" (1 Corinthians 6:20), the terrible price of the never-equaled suffering and the uniquely cruel death of the sinless Son of man. "For to me to live is Christ" (Philippians 1:21). HMM