He that overcometh - See the notes on Revelation 2:7.
Shall inherit all things - Be an heir of God in all things. See the notes on Romans 8:17. Compare Revelation 2:7, Revelation 2:11, Revelation 2:17, Revelation 2:26; Revelation 3:5, Revelation 3:12, Revelation 3:21.
And I will be his God - That is, forever. He would be to them all that is properly implied in the name of God; he would bestow upon them all the blessings which it was appropriate for God to bestow. See the 2-Corinthians 6:18 note; Hebrews 8:10 note.
And he shall be my son - He shall sustain to me the relation of a son, and shall be treated as such. He would ever onward sustain this relation, and be honored as a child of God.

Inherit all things - Here he had no inheritance; there he shall inherit the kingdom of heaven, and be with God and Christ, and have every possible degree of blessedness.

He that overcometh,.... All spiritual enemies, sin, Satan, and the world, the antichristian beast, his image, mark, and number of his name; who is more than a conqueror through Christ; one that perseveres to the end, notwithstanding all temptations, trials, and difficulties; See Gill on Revelation 2:7,
shall inherit all things; the kingdom of Christ in the new Jerusalem state, and all things in it; heaven, eternal glory and happiness, and everlasting salvation; yea, God himself, who is the portion, and exceeding great reward of his people, and will be all in all. The Alexandrian copy, and the Vulgate Latin, Syriac, and Arabic versions, read, "these things": the new heaven, and new earth, the presence of God with men, freedom from all evils, and divine refreshments from the fountain of living water before mentioned:
and I will be his God, and he shall be my Son; Christ is not only concerned in predestination to the adoption of children, in making way by redemption for the enjoyment of this blessing, and in the actual donation of it; but he himself, who is the mighty God, is the everlasting Father, and his people are his spiritual seed and offspring, and in his kingdom he will see his seed, and prolong his days; he will long enjoy them, and present them to himself, and afterwards to his Father, saying as in Hebrews 2:13 and though they are now, in the present state of things, the sons of God, yet it does not appear so manifest that they are, or at least what they shall be; but in this new and glorious state of things, it will be abundantly manifest that they are the sons of God and seed of Christ; and it will be known how glorious they are, and shall be, when they shall see Christ in his glory, and be like him; who will now be , "the Father of the world to come", as the Septuagint render the phrase in Isaiah 9:6.

He that overcometh--another aspect of the believer's life: a conflict with sin, Satan, and the world is needed. Thirsting for salvation is the first beginning of, and continues for ever (in the sense of an appetite and relish for divine joys) a characteristic of the believer. In a different sense, the believer "shall never thirst."
inherit all things--A, B, Vulgate, and CYPRIAN read, "these things," namely, the blessings described in this whole passage. With "all things," compare 1-Corinthians 3:21-23.
I will be his God--Greek, "I will be to him a God," that is, all that is implied of blessing in the name "God."
he shall be my son--"He" is emphatic: He in particular and in a peculiar sense, above others: Greek, "shall be to me a son," in fullest realization of the promise made in type to Solomon, son of David, and antitypically to the divine Son of David.

He that overcometh - Which is more than, "he that thirsteth." Shall inherit these things - Which I have made new. I will be his God, and he shall be my son - Both in the Hebrew and Greek language, in which the scriptures were written, what we translate shall and will are one and the same word. The only difference consists in an English translation, or in the want of knowledge in him that interprets what he does not understand.