…and in Him you have been made complete, and He is the head over all rule and authority;
To be complete here means to fill to the full, be satisfied. You will only be satisfied in life when Jesus is what you are focused on. Everything else will leave you feeling empty and unfulfilled. If your happiness and joy in life is found in what you posses, or in the approval of other people whether they like you or not, it will be temporary, for what is seen in the natural is subject to change.
If we think anything other than Jesus is going to fulfill our life and make us complete, we are still living under the deception of Adam and Eve, looking to God’s creation to find joy and contentment instead of the Creator Himself, through whom all things were created. Don’t worship the creation, including other people, for there is only One who will bring full value and worth and satisfaction to your life, the One who gave His life for you.
As 1 John 2:15 tells us we are not to love the world, nor the things in the world. If we do then we do not have a love for the Father. You cannot love God and love the world at the same time. Set your affection on God not on worldly things. Make Him your priority every day. When your heart is set on the Lord you will walk in the only thing that will make you complete, Him.