You should have practiced the latter, without neglecting the former.

Emphasy on "WITHOUT NEGLECTING THE FORMER"

What is the former thing he mentioned? Paying tithes of all.

By Jesus statement, he meant that the Pharisees were neglecting justice, mercy and faithfulness, but paying tithes, that they should have practiced both Justice, mercy, faithfulness and tithing.

It's such a clear statement brethren.

Nonetheless, Not paying of tithes is not a sin, tithing in the new testament is a mystery. If you believe in it, that by doing so, God will open windows of heaven for you and rebuke devourers, fine. If you don't believe, still fine.

But note that when Abraham paid tithes, he wasn't an Israelite, Israelites came out from him, including Moses,so when they say that TITHING was for Israelites, they should explain why Abraham paid it when he wasn't an Israelite.

Every blessings pronounced in the Bible are still valid, whether in Moses era of Christian era.

Job 36:11

If they obey and serve him, they shall spend their days in prosperity, and their years in pleasures.

Malachi 3:10-11

10 KJV: Bring ye all the tithes into the storehouse, that there may be meat in mine house, and prove me now herewith, saith the Lord of hosts, if I will not open you the windows of heaven, and pour you out a blessing, that there shall not be room enough to receive it.
11 KJV: And I will rebuke the devourer for your sakes, and he shall not destroy the fruits of your ground; neither shall your vine cast her fruit before the time in the field, saith the Lord of hosts.

All the blessings above a valid till the end of the world, if we harken to them.
Shalom!