It depends on what is meant by "observe".
If you mean "to depend on for salvation"....then that is vanity.
If you mean "Study, know the roots and significance of our Messiah"....then there is great value in that.
“For whatever was written in earlier times was written for our instruction, so that through perseverance and the encouragement of the Scriptures we might have hope.” (Romans 15:4)
“All Scripture is inspired by God and profitable for teaching, for reproof, for correction, for training in righteousness;” (2 Timothy 3:16)
““It shall be with him and he shall read it all the days of his life, that he may learn to fear the LORD his God, by carefully observing all the words of this law and these statutes,” (Deuteronomy 17:19)