From the first-century Christian songs scholars believe are embedded in New Testament (e.g., Philippians 2:6-11; Ephesians 5:14; Colossians 1:15-20; 1 Timothy 1:17; etc.), we can infer that the earliest Christian hymns were heavily laden with doctrinal content. Their creed-like wording emphasized the common ground all Christians shared, and singing them served to bind Christians together in unity.
Today’s Christian songs tend to be less doctrinal and more–what? Either focused on praise to God or on encouraging the believer. Nothing wrong with that, but for the most part we seem to have lost this means both of instructing one another on the sine qua non’s of our faith and of reminding each other what we share in Christ.
Nevertheless, we live in an era rich with great hymns that are spiritually enriching, encouraging, and uplifting, with more being written all the time. For this we should be most grateful.