Jeremiah is still applicable today, as is all the Bible because God never changes. When the remnant of Judah asked Jeremiah to pray for them, promising that they would do according to all that God would say, he did so. But they did not keep their promise and ended up dying by the sword, famine, and pestilence (Jerimiah 42:18-22).
Today we have the Bible in its entirety to tell us all God wants us to do, yet so few actually do according to all the Lord our God tells us. They do not obey the Lord, keeping all His commandments, thereby negating the 'sign between Me and thee' (Exodus 31:13). Yet He keeps trying to get our attention, using anything and everything! Even so, most allow Him to be superseded by other people they consider 'more educated so they must have better knowledge' or 'they have the time to study as we pay them to study the Word': mostly because it is more convenient to do things the way of the world, changing it all just a tiny bit by throwing in a little bit of the Bible without integrity. This is the epitome of the gate and the broad way which lead to destruction (Matthew 7:13-14)! No one can have better knowledge of what He requires than God Himself, through the writings He has left us and through His Holy Spirit he gave us, to teach us. If we don't heed Him, refusing to worship Him as He says to instead of mixing in the the way the world worships their gods (Deuteronomy 12:30-32), we are worshiping false deities which the enemy, Satan, has put into place instead of worshipong God.
There are seven main High Sabbaths and festivals given to us by our Lord God, in addition to the weekly Sabbath. These are what He wants us to worship Him by celebrating, not Christmas, Easter, and other holidays derived by mixing in His name with pagan deities. It all boils down to whether we are in love with our Lord God, or the world...