In other words, the appearance of godliness, but the heart intent is not there. They fasted, but they bickered and fought. They fasted but they acted mean. They went to church, but did not take God seriously or kept Him with them while going about their daily business.
Today some Christians do the same thing. Why do we act mean towards each other? Why do we hold grudges against each other? It takes a lot of love and mercy to be a true believer in Christ.
I believe what Isaiah is saying here correlates with Jesus’ cursing of the scribes and Pharisees in Matthew 23. Only Jesus says it much harsher drop down to verse 25.
Woe to you, scribes and Pharisees, hypocrites! For you cleanse the outside of the cup and of the dish, but inside they are full of extortion and excess. Blind Pharisee! First cleanse the inside of the cup and of the dish, so that the outside of them may be clean also. Woe to you, scribes and Pharisees, hypocrites! For you are like whitewashed tombs, which indeed appear beautiful outside, but inside they are full of dead men's bones, and of all uncleanness. Even so you also appear righteous to men outwardly, but inside you are full of hypocrisy and iniquity.Matthew 23:25
Now compare Isaiah 58:13
If you turn your foot because of the Sabbath, from doing what you please on My holy days, and call the Sabbath a delight, the holy of Jehovah, honorable; and shall honor Him, not doing your own ways, nor finding your own pleasure, nor speaking your own words…
They are almost exactly the same.
Didn't they learn anything in those 700+ years since Isaiah lived?
Praise God that believers today have the Holy Spirit funneling as much of God's love and mercy into our hearts that we allow to settle there. It's a choice, yes, but it is a burden-relieving choice because we don't have to do it alone! God does it for us if we just let Him.