"Then Peter answered and said to Him, 'See, we have left all and followed You. Therefore what shall we have?' So Jesus said to them, 'Assuredly I say to you, that in the regeneration, when the Son of Man sits on the throne of His glory, you who have followed Me will also sit on twelve thrones, judging the twelve tribes of Israel. And everyone who has left houses or brothers or sisters or father or mother or wife or children or lands, for My name's sake, shall receive a hundred fold, and inherit eternal life. But many who are first will be last, and the last first'" (Matt. 19:27-30).
Peter and the others are struggling to understand Jesus' teaching on riches. Thus, it is reasonable for them to ask what they will receive for leaving everything and everyone to follow Him. They want to know more about the "treasure in heaven" that Jesus promised (cf. 19:21).
The word "regeneration" is used only one other time in the New Testament (cf. Titus 3:5). The "regeneration" is probably a reference to the time period between Pentecost and the second coming of Christ (the time in which we now live). It is during this time that men can be added to the church by being baptized into Christ, thereby becoming a "new creation" or a "new generation" (i.e., regeneration; II Cor. 5:17). During this period, Jesus sits on the throne of glory at the right hand of the Father (cf. Mark 16:19; Heb. 8:1; I Cor. 15:24-28). Notice that the apostles were not promised "thrones of glory," but simply "thrones." The idea seems to be that Jesus will make the apostles judges; that is, during their lives they would be guided into all the truth and thus authorized to establish the laws and practices of the church (cf. John 16:13,14; 14:26; Matt. 16:18,19; 18:18). They did such then in person through their teachings, and today they judge through their inspired writings (i.e., the New Testament). It is in this sense that they are "judging the twelve tribes of Israel" (i.e., the church, spiritual Israel; cf. Rom. 2:28,29).
This passage must be understood metaphorically (as suggested above). The apostles are not literally sitting on thrones any more than they are literally judging the physical twelve tribes of Israel! Also, the twelve who heard Jesus at this time were not all "enthroned." Judas killed himself before Pentecost. The idea of twelve judges over twelve tribes simply indicates that judgment will be sufficient for the need (i.e., the inspired word of God is sufficient for judgment; cf. II Tim. 3:16,17; John 12:48).
Jesus' list of various earthly ties in Matthew 19:29 indicates that the self-denial of discipleship must be complete. One's dedication to the kingdom of God must be supreme above any other relationship or possession (cf. Matt. 6:33; 10:37).
The Lord offers no assurance or guarantee of physical wealth to His faithful followers. But, there is the promise that when we make tremendous sacrifices for God, He will fill that void with greater blessings (both temporally and eternally). Such ones "shall receive a hundredfold, and inherit eternal life." The return, of course, will not be in like-kind (e.g., houses for house, fathers for father, etc.), but spiritual relationships and blessings (both now and forever) will compensate abundantly for whatever has been given up physically (cf. Matt. 12:49,50). These joys will be mingled with persecution (cf. Mark 10:30) which will enable patience to be produced through the testing of one's faith (cf. James 1:2-4).
If the rich, young ruler had sold all and given to the poor, he would have been filled up and overflowing with far greater blessings (e.g., hope, joy, peace, salvation, etc.)! Sadly, his love of his wealth blinded him to this truth; many today are just as blind.
"But many who are first will be last, and the last first" (cf. Matt. 20:8,16). This statement should not necessarily be understood as a truth that applies absolutely since Jesus used the word "many," not "all." It appears that Jesus is issuing a warning to His disciples. He had just promised great things to His faithful followers, but He doesn't want them to fall into the sin of exalted pride as a result. Jesus elaborates upon this thought in the parable that follows.