Revelation 4:6-8 ESV

and before the throne there was as it were a sea of glass, like crystal.
And around the throne, on each side of the throne, are four living creatures, full of eyes in front and behind: the first living creature like a lion, the second living creature like an ox, the third living creature with the face of a man, and the fourth living creature like an eagle in flight. And the four living creatures, each of them with six wings, are full of eyes all around and within, and day and night they never cease to say,
                                                 “Holy, holy, holy, is the Lord God Almighty,
                                                          who was and is and is to come!”

The four living creatures are the four sides of spiritual maturity.

The face of " a lion " that’s authority. I have spiritual authority when I really know who I am.
The foundation of my life is The Rock, The Lord Jesus Christ. The realm of spiritual authority is a
Kingdom realm. Where The Spirit of The Lord is Lord there is authority and liberty. (2 Cor 3:17)

The face of "an ox ". My life is submitted sacrificially to the Lord. (Mat 11:29)
Given to the Lord. Present yourselves as a living sacrifice. (Rom 12:1-2)
I am yoked with The Lord ever waiting, sensitive and responsive to the moving of His Spirit 

The face of " a man ". I am a new creature in Christ Jesus (2Cor 5:17)
I am in a place of communion and fellowship with Him..The Lord can share his heart with me.
I can relate and understand what is being imparted in the Spirit

The face of " an eagle " This speaks of Spirituality.  I have been lifted brought up into that place with Him We shall mount up with wings (Isaiah 40:31). We have the divine capacity to ascend into the realm of the spirit. They that wait upon the lord... shall mount up with wings as eagles. I can move in the spirit. In Him we live and move (Acts 17:28) Spiritually...thou hearest the wind and knows the sound (John 3:8) as I become sensitive to the manifest presence of the Lord and respond to that, then I am moving in harmony with Gods eternal purpose.

He has made us partakers of a divine nature. (2 Peter 1:4)
That the character of Christ might be formed in us (Gal 4:19)

The four living creatures are a picture of the New Testament Overcomer.

Revelation 3:20-22 KJV

20 Behold, I stand at the door, and knock: if any man hear my voice, and open the door, I will come in to him, and will sup with him, and he with me.
21 To him that overcometh will I grant to sit with me in my throne, even as I also overcame, and am set down with my Father in his throne.
22 He that hath an ear, let him hear what the Spirit saith unto the churches.