d) Jesus did not have long life. Missionaries say he had long life in heaven, but that, again, is stretching the meaning of the word.
Isaiah Chapter 53
8: He was taken from prison and from judgment: and who shall declare his generation? for he was cut off out of the land of the living: for the transgression of my people was he stricken.
9: And he made his grave with the wicked, and with the rich in his death; because he had done no violence, neither was any deceit in his mouth.
10: Yet it pleased the LORD to bruise him; he hath put him to grief: when thou shalt make his soul an offering for sin, he shall see his seed, he shall prolong his days, and the pleasure of the LORD shall prosper in his hand.
The messiah is said to die, and then have his days prolonged. Thus the text is not saying that the Messiah would have a long life before his suffering and death (as the author of your argumnet implies), but after! This is a reference to the messiah being resurrected. Jesus days have been prolonged. The Messiah after he suffers is to reign on David's throne according to prophecy.
1. Jesus Christ is still "of the seed of David" This must be so for him to rule on David's throne. The phrase "of the seed of David" refers to him being a fleshly human decendant of David.
2 Samual Chapter 7
[12] And when thy days be fulfilled, and thou shalt sleep with thy fathers, I will set up thy seed after thee, which shall proceed out of thy bowels, and I will establish his kingdom.
[13] He shall build an house for my name, and I will stablish the throne of his kingdom for ever.
[14] I will be his father, and he shall be my son. If he commit iniquity, I will chasten him with the rod of men, and with the stripes of the children of men:
[15] But my mercy shall not depart away from him, as I took it from Saul, whom I put away before thee.
[16] And thine house and thy kingdom shall be established for ever before thee: thy throne shall be established for ever.
Psalm 132
[11] The LORD hath sworn in truth unto David; he will not turn from it; Of the fruit of thy body will I set upon thy throne.
Acts chapter 2
[29] Men and brethren, let me freely speak unto you of the patriarch David, that he is both dead and buried, and his sepulchre is with us unto this day.
[30] Therefore being a prophet, and knowing that God had sworn with an oath to him, that of the fruit of his loins, according to the flesh, he would raise up Christ to sit on his throne;
[31] He seeing this before spake of the resurrection of Christ, that his soul was not left in hell, neither his flesh did see corruption.
[32] This Jesus hath God raised up, whereof we all are witnesses.
Romans Chapter 1
[3] Concerning his Son Jesus Christ our Lord, which was made of the seed of David according to the flesh;[4] And declared to be the Son of God with power, according to the spirit of holiness, by the resurrection from the dead:
Revelation Chapter 22
[16] I Jesus have sent mine angel to testify unto you these things in the churches. I am the root and the offspring of David, and the bright and morning star.
2. David will have a son to reign on his throne (Jeremiah 33:21). Christ is this son (Luke 20:44). He is the son of David when He is at the right hand of the Lord (hense He is human in heaven).
Jeremiah Chapter 33
[17] For thus saith the LORD; David shall never want a man to sit upon the throne of the house of Israel;
[18] Neither shall the priests the Levites want a man before me to offer burnt offerings, and to kindle meat offerings, and to do sacrifice continually.
[19] And the word of the LORD came unto Jeremiah, saying,
[20] Thus saith the LORD; If ye can break my covenant of the day, and my covenant of the night, and that there should not be day and night in their season;
[21] Then may also my covenant be broken with David my servant, that he should not have a son to reign upon his throne; and with the Levites the priests, my ministers.