Isaiah 56:3

(Verse 3.) And let not the son of the stranger, who adheres to the Lord, say, 'The Lord will surely separate me from His people.' And let not the eunuch say, 'Behold, I am a dry tree.' LXX: Neither let the foreigner, who is joined to the Lord, say, 'The Lord will surely separate me from His people.' And let not the eunuch say, 'I am a dry tree.' Those who understand this passage humbly refer it to proselytes from the nations and truly to eunuchs, as it is said that even strangers, if they receive the law of the Lord and are circumcised, and eunuchs, like the eunuch of Queen Candace (Acts 8), who could not even be idle on a journey, and while he was seeking an interpreter of the reading, found Christ whom he was seeking, may not be excluded from the salvation of God. But this, they say, is said against the Jews, who boast of the nobility of their lineage, and claim to be descendants of Abraham, and believe those to be blessed who have offspring in Zion and dwellers in Jerusalem (John VIII). But we, who were previously interpreted as thorns and thistles and κονύζη and στοιβὴν (Above, to chapter LV), we now understand to be turned into fir trees, cypresses, and myrtle trees, and the same people are being challenged in regard to the faith of the Gospel: which they should not despair of, as long as they adhere to the Lord; and they should not consider themselves separated from God's people. For all who have been baptized in Christ have clothed themselves with Christ (Galatians 3:27). There is neither Jew nor Greek, there is neither circumcision nor uncircumcision, barbarian, Scythian, slave, nor free, but Christ is all and in all (Colossians 3:11). And it is written in Deuteronomy: Rejoice, O Gentiles, with His people, that is, the God who had the prior people of the Jews (Deuteronomy 33:43). Those who come from the East and West will rest in the bosom of Abraham. […]

Those who please me are those who choose to be eunuchs voluntarily.… Who can receive this teaching, let him receive it. It is a matter of great faith and great virtue to be the purest kind of temple of God, in that one dedicates oneself completely to the Lord as a burnt offering and to be holy in body as well as spirit. Those are eunuchs who, thinking themselves to be "dry trees" because of their infertility, hear through Isaiah that instead of sons and daughters they will have a place prepared in heaven. Of this sort were Ebedmelech in Jeremiah and that eunuch of Queen Candace.

The stranger who comes before the Lord should not say, "The Lord will surely cut me off from his people." For it will not be because he is foreign in the sense of not having Israelite blood therefore that he will be without a share in the gifts from the Lord, the intimate and spiritual relationship with him. But if he clings to the Lord in his domestic affairs and his friendships, he will be made to belong in the holy people and to the royal priesthood and to the inheritance of God. He will be numbered among the children of Abraham. For not all from Israel are Israel as most-wise Paul said: not all the progeny are the seed of Abraham, but the children of the promise are reckoned as descendants.

Second, he sets out the universality of this utility: and let not the son of the stranger. And first, he excludes the desperation of some who seemed unworthy, either because of defect of race, because they were not of the race of Israel: that adheres …

The stranger - The stranger, the Gentile, who by birth is a stranger to God, that hath turned from dumb idols to the living God. The eunuch - Who is here joined with the stranger, because he was forbidden to enter into the congregation of the Lord, Deut. xxiii, 1.