Yes, Jesus told his followers that, but today we have a thousand different Christian denominations around the world, all claiming that their way is the right way.
The Apostle Paul says at 1st Corinthians 1:10 :"I appeal to you, brothers, in the name of our Lord Jesus Christ, that all of you agree with one another so that there may be no divisions among you and that you may be perfectly united in mind and thought."
You see from this scripture that Christians are to be fitly united in the same mind and the same line of thought, with absolutely no divisions. This is a commandment from Paul, not a recommendation. Yet, Christians fight wars against each other because they believe their belief system is the correct way and only way to believe.
So, out of the 1,000 Christian denominations in the world, what Christian denomination is for Jesus, and which ones are against him?
The Bible says at Ephesians 4:5 that there is "one Lord, one faith, one baptism;.."
Again, the question can be asked: What "one faith" is the true religion?
First of all, Christ addresses the issue of people who do things in Christ's name but who do not follow exactly with the Apostles in Luke 9:49-50:
49 John answered, “Master, we saw someone casting out demons in your name, and we tried to stop him, because he does not follow with us.” 50 But Jesus said to him, “Do not stop him, for the one who is not against you is for you.”
The "thousands of denominations" is a really old Roman Catholic canard as well. First, lots of them are liberal non-churches who are only nominal Christians (UCC, PC(USA), EPCUSA, etc.). Secondly, lots of the denominations are simply national divisions, such as the Presbyterian Church in America as opposed to the Free Church of Scotland or the Presbyterian Church in Australia. Also, within a country divisions within a broader denomination (such as the Orthodox Presbyterian Church as opposed to the Presbyterian Church in America) is because the liberal domination of the primary denomination in a country. In this country, the PC(USA) has become more and more liberal, causing Evangelicals to split with it over the course of almost a century now, and that continues to this day. In these cases, the denominations often have agreements that basically make them one denomination for all purposes besides church government.
In the end, there are only really around eight denominations, which all recognize each others' claims to being Christian and do not deny the others' Christianity: Baptist, Presbyterian, Reformed/Low Church Anglican, Continental Reformed (arguably under the Presbyterian banner or visa versa), Lutheran, Anabaptist, Congregationalist, and broader Evangelical "non-denominational" churches. Outside of this, the divisions are either significant enough to deny the others' Christianity, or not worthy of being labeled a separate denomination.