‘For in (or ‘by') him were all things created, in the heavens and on the earth, things visible and things invisible, whether thrones or dominions or principalities or power, all things have been created through him and unto him, and he is before all things and in him all things hold together.'
Jesus as ‘the Firstborn' created all things. Paul is careful to include those beings which existed before the world was created, and to exclude nothing. They were created through Him, and the purpose of their creation was His own benefit and satisfaction (‘unto Him'). Then, to make matters even clearer he says, ‘He is before all things' ('autos 'estin pro panton). He existed before all things, and takes precedence before all things. He is supreme over all, permanently and unceasingly. And He sustains and holds together all things.
This proclamation of Christ as the creator of all things is found elsewhere, in Hebrews 1:2 ‘through Whom also He made the worlds', in John 1:3, ‘all things were made through Him and without Him was not anything made that has been made', and in 1 Corinthians 8:6, ‘one Lord Jesus Christ through Whom are all things'.
‘In (or ‘by') Him were all things created.' Paul does not qualify this, he expands on it. It does not only include earthly creation but the creation of all heavenly beings. Note that He is not said to be the ‘first-created (protoktisis). As the ‘firstborn' of God He existed before creation.
If we translate ‘in Him' (the preposition can mean either) he is the sphere in which all things were created, and thus ‘bigger' than them all. If we translate ‘by Him' He was the source of that creation. Usually creation is said to be ‘through Him' (see paragraph above) which may support translating ‘in Him' here. The verb ‘created' is in the aorist tense signifying a once for all action. Compare later in the verse where it is in the perfect tense, signifying a creation that endures to the present.
‘In the heavens and on the earth.' He then expands this to include all supernatural beings and everything, whether visible or invisible. ‘Thrones, or dominions, or principalities, or powers' represents all authority wherever it may be, including Satan himself. Nothing is outside His creation or His control. Ancient religions invented many demi-gods and divine beings, probably in awareness of these supernatural authorities, but whatever they be, says Paul, He is over them all.
‘In Him all things hold together.' All is sustained by Him. He has but to withdraw His hand and the universe will collapse within itself. In the words of Hebrews 1:3, ‘He upholds all things by His powerful word.'