OK let's start out like this. In a multidimensional universe, you move through dimensions consciously, with your heart and mind. Remember, your body is only a current focal point, but not your whole being.
1D is mineral - yes rocks have a rudimentary consciousness
2D is group souls plants, trees, and animals
3D is an individuated soul - individual consciousness - like us - seemingly separate and alone in our heads and bodies
4D is a merging back to unity through universal, brotherly love (not personal - personal love is 3D construct)
5D is an applied understanding of this that creates wisdom
6D is a combination of compassion and wisdom: Love-Light
7D is a merging back into source at a higher octave of frequency
So, in this type of manifested universe, we are all learning about our consciousness, both as its self and as a unit of a greater whole. Which means that the steps we go through are a growth process and you needs the one before it to understand the one above it. IE: no skipping a grade allowed.
If we are on this earth at this time, we are learning how to make that step from the lonely separated self - the individuated soul, into the awareness of a greater more inclusive whole. To make it into 4D then, the doorway, the lesson, will be one of 'I am not alone'. Both in empathy and in the actual experience of the two way awareness of being in someone else's skin and heart and mind. It will start out gradually where you will be able to 'notice' the person who is sitting next to you and know how and why they are the way they are in that moment. It will build to more than just one other and include group awarenesses and then one day the whole planet will reach that point where they are all of one heart. At that point we will have entered into 4D to stay. Until we reach that point we will be sojourning back and forth. One moment we will be very 3D, into our day and achieving our goals and the next we will be hit with a stunning awareness of the guy next to us on the subway. Get ready for this.
The less fear you have of this, the faster and easier it will begin to happen for you. Either way, it WILL happen. Whether you are ready or not, whether you want it to or not. This awareness will bring us into our hearts as we realize we basically all feel the same way. It will create a world compassion for our fellows on this journey with us. And it will eventually unite our hearts.
This was not meant to be some heavy esoteric article - I just meant to say, be on the lookout for experiences in your life that open the doorways between souls of all kinds - understanding and a feeling of kinship, for this is the marker that means you are on your way. And be happy for each time you experience this, the doorway into 4D opens just a little wider, not only for you, but the planet as well.