And the second question: why do the apostles in the book of acts focus on the humanity of Christ...?
One thing that came to my mind is that realizing and appreciating the humanity of Jesus Christ brings to the forefront the hope that we, too, can live unto God in holiness and power by His Spirit through the Holy Spirit given to us. It brings forth in the mind the issue of the light of the life of God in an "earthen vessel", even Jesus - and our call and duty, as the "temple of God", to have and reveal the same (think: "let your light so shine..." - and we know who is our light and life if we are in Christ).
Though I do believe that Jesus was and ever is fully God, I do also believe that He was and is evermore fully man, too. He is the completion (in one man) and the seed of the Divine thought and purpose. And He is our means, by the Spirit He supplied to us, to achieve the same end - through "vital union" with Him by the Holy Spirit.
Focusing on His Divinity surely has benefits, no doubt. But it is seeing Him as the perfect and representative man (God's representative man, both as an end in mind and a means of achieving this end) that we are both convicted of our coming short of the mind and word of God, and are also encouraged that there is hope for us in the arm of the LORD being revealed in (and ultimately through) us.
If Jesus, by the power of the Father, through the Holy Spirit, by way of humility and dependence upon Him ("Him", I say, for the Two are surely One), can be such as God can receive and highly exalt and justify and remain Just and retain His Glory in doing so - so can we, through Him, if we abide and walk in Him and live in and through Him, be glorified together with Him!
What hope! It is Jesus and the Power of God working in us through faith in Him and not we ourselves!
But the more immediate takeaway (and perhaps more urgent and vital to the Glory of God and salvation of souls) is this: that God can and must be glorified not only in, but through us - by the light of the life of Jesus being seen in His House as He is allowed to live and shine through us! We have a high and holy calling - not just a high and holy message.
Like Jesus, our Example, we too are to be "the word made flesh" - through Him and His ministry of the Spirit (the law written on the heart) and for His glory!
Also, just a "heads up" - I understand what you are saying when you speak of "the divine side" of Jesus, but others may accuse you of "heresy" for implying that Jesus was "half God and half man" as opposed to "fully God and fully man"... ;)
h/t: T. Austin-Sparks and B.H. Clendennen