Yes I know that sounds really lame, but bear with me while I explain why it's important.
The Free Church is theologically conservative, but has also been historically energetic. They set up New College at the University of Edinburgh, which now hosts the School of Divinity - that is, the university's theological faculty. They sent missionaries to Africa, India (Calcutta, Bombay, Poona and Madras), Canada, Australia (!) and the Middle East. Their theology was probably the closest to the Old Princeton Presbyterianism of Charles Hodge and B. B. Warfield.
A lot (most? all?) of this energy has come from the Free Church's theological strength - their focus on the Bible, allied with a thoroughgoing Westminster Calvinism. An aspect of that theological strength has been a conservative view on the Regulative Principle - the view that Sunday church worship (and all of life) must be regulated by the Bible. If it's not permitted in scripture, it's not permitted in church. That's why this church historically hasn't used musical instruments, or sung anything beyond Psalms - which of course are inscripturated songs therefore permissible.
But now, as noted above, they've permitted musical instruments and songs beyond the Psalms.
I think this is a step forward, in that I don't subscribe to such a biblically prescriptive view of the regulative principle as noted above. I think the Bible gives us principles which regulate our response to God - our "worship" - in any and every situation. But I also think God gives us the responsibility of thinking deeply about how to apply those principles in any particular historical and cultural context.
So, let's speak to and teach and admonish one another through psalms, hymns, and Spiritual songs (Eph 5:19; Col 3:16). God breathed out the Holy Scriptures for our teaching, rebuking, correcting and training in righteousness (2 Tim 3:16). So if we meditate deeply upon the Bible, and express Biblical teaching in songs that are carefully crafted so that they're easy to sing, memorable, and with tunes which fit the mood of the words, then we'll be achieving what Paul means in these verses. I think this step by the Free Church will lead to more evangelism, and more authentic worship - worship which is simultaneously biblically faithful, culturally engaged, and deeply personally satisfying.
But of course I could be wrong. This could be a step backwards - a compromising with culture, a loss of biblical and theological clarity, the beginning of the end. We'll have to wait another 50 or so years and see.