Matthew makes is clear that no one knows the hour,
“However, no one knows the day or hour when these things will happen, not even the angels in heaven or the Son himself. Only the Father knows. (24:36)
That it will be like the days of Noah, when people thought Noah daft to be building an Ark when there was no sign of rain, and so ignored him,
People didn’t realize what was going to happen until the flood came and swept them all away (24:39)
So we must learn from this and not make the same mistake,
“So you, too, must keep watch! (24:42)
You also must be ready all the time, for the Son of Man will come when least expected. (24:44)
Most often, the coming of the Son of Man is understood as an apocalyptical future event. Wesley's hymn Lo, he comes with clouds descending, captures the mood as reflected in the Book of Daniel 7:13 echoed in Revelation 1:7:
"Every eye shall now behold Him
Robed in dreadful majesty
Those who set at naught and sold Him
Pierced and nailed Him to the tree
Shall the true Messiah see"
So what should we understand by the coming of the Lord? As I said, it is often understood as the second coming. But the Bible doesn't use that term. Of the Gospel writers only Matthew uses the Greek term parousia, the word used in verse 37 and 39 of in chapter 24. But he does only use it four times in total. In the letters of the New Testament, Paul uses the same term twelve times, Peter three times, James twice and John once; mostly always referring to 'the coming of our Lord Jesus Christ', and there is at least one occasion where Peter refers to that coming as first coming of Jesus, an even which had already happened:
16 For we did not follow cleverly devised stories when we told you about the coming of our Lord Jesus Christ in power, but we were eye-witnesses of his majesty. (1 Peter 1)
So parousia is no doubt the correct term, and it can relate to the past, present and the future. But what does the word mean? Strong's Concordance tells us it means a being near, ie an advent, a coming or presence.
Paul uses it to describe the comfort that he experienced with the coming of Stephanus and of the coming of Titus:
17 I was glad when Stephanas, Fortunatus and Achaicus arrived (1 Cor 16)
6 But God, who comforts the downcast, comforted us by the coming of Titus, 7 and not only by his coming but also by the comfort you had given him. (2 Cor 7)
So that being near is a comforting presence. When Jesus spoke of his departure from this world he promised the coming of the Holy Spirit as a Comforter, an Advocate who would teach his disciples all things and guide them in truth.
So the coming of the Lord Jesus, means that his presence is able to be with us not only now and forever but also in our past. There are things in our past, the memories of which might still trouble us. Jesus is able to journey back with us, to that troubling time and bring healing or acceptance of the situation or a letting go of it or even forgiveness if that is what is needed. I've seen it happen - people set free from the nightmares of their past by a God who cares for them and wants to see them made whole because he loves them. Is there something in your past that you'd like dealt with? Then Jesus is able to come into that situation with you even now as you ask him to.
And this answers the question of why does he need to come. He comes to save. He comes as Saviour. Yes, he comes as Guide and Comforter but also as Saviour, to save people from their own sin and from the effects of sin on them. We all need a Saviour and Jesus is the only one who can give us the guarantee that sins are forgiven. You won't find that guarantee in other religions.
May his being near be real to you today.
May he save you from all that harms you.
May he use you in bringing his saving and comforting presence to others in this world.