And God, which knoweth the hearts, bare them witness, giving them the Holy Ghost, even as he did unto us;

Wesley's Notes

15:8 God bare them witness - That he had accepted them, by giving them the Holy Ghost.

Jamieson-Fausset-Brown Bible Commentary

8. God, which knoweth the hearts-implying that the real question for admission to full standing in the visible Church is the state of the heart. Hence, though that cannot be known by men, no principle of admission to church privileges which reverses this can be sound.

Matthew Henry's Concise Commentary

15:7-21 We see from the words purifying their hearts by faith, and the address of St. Peter, that justification by faith, and sanctification by the Holy Ghost, cannot be separated; and that both are the gift of God. We have great cause to bless God that we have heard the gospel. May we have that faith which the great Searcher of hearts approves, and attests by the seal of the Holy Spirit. Then our hearts and consciences will be purified from the guilt of sin, and we shall be freed from the burdens some try to lay upon the disciples of Christ. Paul and Barnabas showed by plain matters of fact, that God owned the preaching of the pure gospel to the Gentiles without the law of Moses; therefore to press that law upon them, was to undo what God had done. The opinion of James was, that the Gentile converts ought not to be troubled about Jewish rites, but that they should abstain from meats offered to idols, so that they might show their hatred of idolatry. Also, that they should be cautioned against fornication, which was not abhorred by the Gentiles as it should be, and even formed a part of some of their rites. They were counselled to abstain from things strangled, and from eating blood; this was forbidden by the law of Moses, and also here, from reverence to the blood of the sacrifices, which being then still offered, it would needlessly grieve the Jewish converts, and further prejudice the unconverted Jews. But as the reason has long ceased, we are left free in this, as in the like matters. Let converts be warned to avoid all appearances of the evils which they formerly practised, or are likely to be tempted to; and caution them to use Christian liberty with moderation and prudence.