Had seen the grace of God - The favor, or mercy of God, in converting sinners to himself.
Was glad - Approved of what had been done in preaching the gospel to the Gentiles, and rejoiced that God had poured down his Spirit on them. The effect of a revival is to produce joy in the hearts of all those who love the Saviour.
And exhorted them all - Entreated them. They would be exposed to many trials and temptations, and he sought to secure their firm adherence to the cause of religion.
That with purpose of heart - With a firm mind; with a fixed, settled resolution that they would make this their settled plan of life, their main object. A purpose, πρόθεσις prothesis, is a resolution of the mind, a plan, or intention, Romans 8:28; Ephesians 1:11; Ephesians 3:11; 2Ti 1:9; 2 Timothy 3:10. It is especially a resolution of the mind in regard to future conduct, and the doctrine of Barnabas here was, undoubtedly, that it should be a regular, fixed, determined plan or design in their minds that they would henceforward adhere to God. Such a plan should be formed by all Christians in the beginning of their Christian life, and without such a plan there can be no evidence of piety. We may also remark that such a plan is one of the heart. It is not simply of the understanding, but is of the entire mind, including the will and affections. It is the leading principle; the strongest affection; the guiding purpose of the will to adhere to God, and, unless this is the prevalent, governing desire of the heart, there can be no evidence of conversion.
They would cleave - Greek: that they would remain; that is, that they would adhere constantly and faithfully attached to the Lord.