Then why would anyone follow his teachings?
Baha'u'llah did not make a mistake, because He, like Jesus, was infallible.
But just as with Jesus, some people misunderstand what Baha'ullah meant by what He said.
Just as with Jesus, we have to read other scriptures that Baha'u'llah has written, not just one verse.
They are not contradictory if we understand what they mean.
Even the most avid Christians I know who have degrees in theology do not believe the Bible is inerrant. It can't be, given how it came to be recorded. Some authoritative Baha'i positions on the Bible are as follows and more can be found on that link at the bottom.
From the Writings of Bahá'u'lláh:
The Four Gospels were written after Him [Christ]. John, Luke, Mark and Matthew - these four wrote after Christ what they remembered of His utterances.
(From a previously untranslated Tablet)
From Letters Written on Behalf of the Guardian:
...The Bible is not
wholly authentic, and in this respect is not to be compared with the Qur'an, and should be wholly subordinated to the authentic writings of Bahá'u'lláh.
(28 July 1936 to a National Spiritual Assembly)
...we cannot be sure how much or how little of the four Gospels are accurate and include the words of Christ and His undiluted teachings, all we can be sure of, as Bahá'ís, is that what has been quoted by Bahá'u'lláh and the Master must be absolutely authentic. As many times passages in the Gospel of St. John are quoted we may assume that it is his Gospel and much of it accurate.
(23 January 1944 to an individual believer)
When 'Abdu'l-Bahá states we believe what is in the Bible, He means in substance. Not that we believe every word of it to be taken literally or that every word is the authentic saying of the Prophet.
(11 February 1944 to an individual believer)
We cannot be sure of the authenticity of any of the phrases in the Old or the New Testament. What we can be sure of is when such references or words are cited or quoted in either the Quran or the Bahá'í writings.
(4 July 1947 to an individual believer)
Except for what has been explained by Bahá'u'lláh and 'Abdu'l-Bahá, we have no way of knowing what various symbolic allusions in the Bible mean.
(31 January 1955 to an individual believer)
From letters written on behalf of the Universal House of Justice:
In studying the Bible Bahá'ís must bear two principles in mind. The first is that many passages in Sacred Scriptures are intended to be taken metaphorically, not literally, and some of the paradoxes and apparent contradictions which appear are intended to indicate this. The second is the fact that the text of the early Scriptures, such as the Bible, is not wholly authentic.
(28 May 1984 to an individual believer)
...The Bahá'ís believe that God's Revelation is under His care and protection and that the essence, or essential elements, of what His Manifestations intended to convey has been recorded and preserved in Their Holy Books. However, as the sayings of the ancient Prophets were written down some time later, we cannot categorically state, as we do in the case of the Writings of Bahá'u'lláh, that the words and phrases attributed to Them are Their exact words.
(9 August 1984 to an individual believer)
The Bible: Extracts on the Old and New Testaments