The overcoming believers in Christ will inherit the eternal life as a reward to them in the millennium (Matt. 19:28-29; Rev. 20:4-6). To have eternal life and to inherit eternal life are two different things in the New Testament. John 3:16 says that "everyone who believes in Him [the Son] should not perish, but have eternal life." However, Matthew 19:29 says, "And everyone who has left houses, or brothers, or sisters, or father, or mother, or children, or lands for My name's sake, shall receive a hundredfold and shall inherit eternal life." To have eternal life is a matter in the present age; thus, in John 3:16 the Lord Jesus used the present tense of the verb have. However, in Matthew 19:29, the Lord used the future tense of inherit, because the inheriting of eternal life is something for the coming age.
We have eternal life today, and we are enjoying it today. Eternal life certainly is ours today, but we cannot yet say that we have inherited eternal life as our legal possession. To have eternal life, the only requirement is that we believe in Christ (John 3:16; 20:31). However, to inherit eternal life, we must fulfill additional conditions and requirements. One of the conditions for inheriting eternal life is that we must give up all the things of this age (Matt. 19:29).
The inheriting of eternal life in Matthew 19:29 is related to the kingdom. This is proven by the preceding verse, which says that in the regeneration the twelve apostles, who followed the Lord Jesus, will sit on twelve thrones, judging the twelve tribes of Israel (v. 28). To sit on thrones is not something of this age; it is something for the coming kingdom age. In the kingdom age, the overcoming saints will rule as kings sitting on thrones (Rev. 20:4, 6). The context of Matthew 19:29 strongly proves that the inheriting of eternal life is related to the kingdom.
In the millennium, the paradise of God will be the New Jerusalem. The overcoming believers will enjoy Christ as the tree of life in the paradise of God, which is the New Jerusalem in the millennium (Rev. 2:7). During the one thousand years of the kingdom, the New Jerusalem on a small scale will be a special portion, a reward, to the overcoming believers; but in the new heaven and new earth, the New Jerusalem will be greatly enlarged as the common portion of all God's redeemed people.