If you want to understand a thing properly, Go to the Beginning.

Our life in Christ is not a mediocre one, and vs 26 explains deeply the kind of life we have in Christ Jesus.

It says..

Then God said, “Let us make mankind in our image, in our likeness, so that they may rule over the fish in the sea and the birds in the sky, over the livestock and all the wild animals, and over all the creatures that move along the ground.”

Now lets break it down gradually

First keyword to consider is

IMAGE

Image literally means a reflection of a thing, what you see..

Second keyword is

LIKENESS

This means characteristics, attributes of a thing.

Using a Lion as an example..
When a lioness gives birth, a cub is born, a lion of course, but at that level, a goat can embarrass that baby lion assuming the mother isn't around.

Why?
The lion has the image, but doesn't have the likeness. Yes, it looks like a lion, but doesn't have the characteristics yet.

It is important to note that characteristics(likeness) is a product of growth. As soon that baby lion keeps feeding and growing, the likeness gradually starts finding expression until a point where the goat dare not come even 100km close to anywhere the lion lives.

Same way when we get born again, we are now in God's image, but feeding on God's word, spending time with people of like-mind, these takes away some ugly expressions in us and then the behavioural pattern of christ is found in us.

IMAGE WITHOUT LIKENESS WON'T GIVE YOU DOMINION OR RULERSHIP OVER ALL

You can be born again, yet oppressed by satan, but...

IMAGE AND LIKENESS MAKES US TO WORK IN DOMINION OVER ALL.

So lets feeding God's word, keep growing, therein our BEING LIKE CHRIST lies which gives rise to DOMINION.