Paul here mentions two types of evidence of being filled with the Spirit. One concerns prayer and praise in the public gatherings of believers, which indicates that when Christians do not take part in such occasions they are showing signs of not being filled with the Spirit. The other evidence that Paul mentions is in verse 21 and concerns mutual submission. Both these practices indicate that participation in Christian fellowship is the purpose of being filled with the Spirit.
In verse 19, Paul mentions ‘speaking to yourselves’. He does not mean that a Christian speaks to himself; rather he means that Christians are addressing one another when they offer praise to God. When we sing in church, we are not only singing to God, we are also exhorting one another to sing to God. For example, when we sing, ‘come, let us worship him,’ we are to have an awareness that we are addressing one another. (I will explain tomorrow what I think Paul means by psalms, hymns and spiritual songs.)
There is an obvious similarity between a group of drunk people and a group of Spirit-filled Christians and that is that they both love to sing. But the singing of Christians is to be about real matters that involve God and the spiritual life.
Paul also says that a Spirit-filled Christian will sing from the heart. This does not merely mean that he will sing loudly; rather it means that he will sing appropriately with suitable feelings. The apostle also indicates that a Spirit-filled person, when he sings, will have the Lord Jesus in focus. When Paul says that they should make melody ‘to the Lord’, the title ‘Lord’ is a reference to Christ.
Paul then mentions another evidence of a Spirit-filled person, and that is thankful prayer. Gratitude is an essential attitude in a healthy Christian outlook. It is possible that Paul here is reminding his readers that they should be thankful for one another, which fits in with singing to one another (v. 19) and submitting to one another (v. 21).
The final evidence that Paul gives of a Spirit-filled person is mutual submission (v. 21). This verse is a hinge verse in that it is connected to what precedes it (submitting is a participle connected to ‘being filled with the Spirit’) but also introduces what follows. The way that Paul expands the concept of submission in the following verses indicates the importance he gave to it, and reminds us that practical Christian living must be based on doctrinal understanding. Marriage relationships, parental relationships and work relationships, as far as Christians are concerned, require the filling of the Spirit.