For so hath the Lord commanded us, [saying], I have set thee to be a light of the Gentiles, that thou shouldest be for salvation unto the ends of the earth.
Note 2 at Ac 13:47: There is no clear reference in Scripture where the Lord spoke these words to Paul. The Lord did speak to Paul through Ananias about a ministry to the Gentiles (see note 7 at Ac 9:17), and the Lord spoke directly to Paul about being sent to the Gentiles when Paul was in a trance in the temple at Jerusalem (Ac 22:17-21). However, this is not what Paul was referring to.
Paul was not the light to the Gentiles and the salvation for the ends of the earth; Jesus was. This is a quotation from Isa 49:6. Therefore, this is an example of the Lord speaking to Paul through His Word. When we receive revelation from God's Word, it is God speaking to us. It is a more trustworthy method of hearing God speak than an audible voice (2Pe 1:18-20), and it carries a greater blessing (see note 4 at Joh 20:29).