There are two major schools of thought on this. Our charismatic friends tend toward equating the filling of the Spirit with speaking in tongues. I don't believe that they are correct on that because:
- Not everyone has the gift of tongues (1 Cor. 12:30), but everyone is commanded to be filled with the Spirit (Ephesians 5:18).
- While tongues is mentioned as evidence of being filled with the Spirit in Acts 2 and a couple other places in Acts, here in chapter 4, there is no mention of anyone speaking in tongues. Nor is tongues described as "the filling of the Spirit" elsewhere it is mentioned. For example, in Ephesians 5:18ff, evidence of filling of the Spirit includes such things as "speaking to one another with songs, hymns, and spiritual songs," avoiding drunkenness, thankfulness to God, having a God-honoring marriage, a God-honoring master/slave relationship, and obeying one's parents.
- Therefore, I think the filling of the Spirit, while it may be evidenced by tongues speaking, is not equivalent to it.
That fact is a great comfort to me, because I find myself so often in need of fresh filling from the Spirit to accomplish the calling He has given me. Whether in my role as pastor, or as husband, father, or simply as a human being created in God's image, I often fail. I don't always speak as I should, think as I should, or act as I should. Yet God is gracious, granting both forgiveness and fresh filling from the Spirit as often as I fall down. What a mighty, gracious, compassionate God we serve!