It’s great to hear that you are keen to answer your mum’s questions about Christianity. It is true that with the Tower of Babel, God scattered humanity and created language barriers. This was God’s judgement against humanity. Humanity was ganging up to gain significance for itself, apart from God (Genesis 11:4). This was a manifestation of the ultimate human problem: our rebellion against God. Since Adam, humans have wanted to live life our own way, gaining our significance apart from God. The scattering of humanity was one judgement of God but the ultimate judgement against all humans was death and separation from God (Genesis 3:19-24). In our modern world, we can see that this problem of human sin is still entrenched in us and your mum’s observation about the world coming together can indeed sometimes be discerned as a new act of arrogance and fierce desire of autonomy apart from God.
However, what has changed since Babel is that God has made it abundantly clear that he does not want the world to remain in division, confusion and judgement. God has taken active steps to solve our ultimate problem of rebellion. 2000 years ago, God’s son Jesus died on the cross, for us. His death took the judgement that was rightfully on us. If we trust in Jesus, his death is counted as ours and our punishment is thus paid and we are now considered right and reconciled with God. The war with God, as epitomised in Babel, is over because of what Jesus has done.
Thus with this good news, a new era is here. There is a way out of the ultimate judgement. And this good news is to reach all people, giving all people the chance to repent. And it is this good news that the missionaries are proclaiming. The missionaries are thus not going against God’s imposed will (or judgement) of the scattering of humanity; they are in fact working in line with God’s will of having all nations hear the good news of Jesus. And they are primarily concerned with our relationship with God, and not on eradicating cultural diversities, or changing styles of living. Sometimes, this work of the missionaries might mean having to help a culture care for itself better (eg building wells) or changing certain customs which are not in line with genuine worship of God. This does not mean that missionaries should not be sensitive to cultural differences and needs. But ultimately, God is not interested in retaining individual cultures just for the sake of it. His will is that all peoples everywhere should come to hear of Jesus and be radically changed by him, as individuals and as cultures. And God has promised that one day, humanity will again be gathered into one united humanity, this time a humble humanity who worships God gladly and with one voice (Revelation 7:9-12).