Tithing was a part of being a true Jew - giving to God a tenth of one's income.  There were three main tithes in the Old Testament: the sacred tithe (Genesis 14:18-20; Numbers 18:21-24), the tithe at the feasts (Deuteronomy 14:22-27), and the tithe for the poor (Deuteronomy 14:28-29).  Each tithe was an obedient response to God’s command to give the best to Him.  The tithes supplied the personal needs of the priests, and the poor, and was a God-honouring personal or family sacrifice.

The religious leaders of Jesus’ day turned a straightforward command into a complicated religious art-form.  If they grew garden herbs, then 10% of the crop was measured out and given to the priests: and Jesus did not criticise that practice. What He objected to, was the contrast between the physical tithes which everybody could see, and their invisible failures to treat people fairly and to love God by obeying His commands about relationship.  Giving a tithe of mint was easy but sacrificing their time, energy and money for the poor was hard.  The parable of the good Samaritan makes that point well (Luke 10:28-37).

That sort of hypocrisy presents a good public face but does not reflect the heart of the person.  It is common in religion, but it is not spiritual; it is merely acting on a stage (Matthew 6:1-4).  Jesus condemned the 'heart disease' of formalised religion, which measures spirituality by obeying or even ‘gold-plating’ rules, at the expense of developing a personal relationship with God and godly relationships with other people (James 1:26-27).  By saying "Woe to you ...", Jesus was expressing His grief that leading religious figures could be so blind and would judge their hard-heartedness.  

Today, it is also easy for followers of Jesus to fall into hypocrisy without thinking, particularly if their church has expected patterns of worship or service - where nobody notices the slide from true devotion into religious rule-keeping.  Of course, such practices may well help our devotional life by becoming useful spiritual disciplines, but if they become an end in themselves, we risk dislocating ourselves from the life of Christ.  More than that, any publicly observed religious activity can become a smokescreen for spiritual barrenness and be self-deluding - presuming that all is well with God, when the vitality of relationship with Him has disappeared.  What is the remedy?  As Jesus said, concentrate first on developing a living relationship with God and put His love into practice with the people around you, without neglecting to practise those spiritual disciplines which will enable Your love for the Lord to grow more (Matthew 7:24-27; James 1:22-25).