The effect of God's love for mankind was sacrifice and suffering. It cost Him to show us His love and it cost Jesus to show the Father His love for Him and mankind. The Father loves Me because I lay down my life in order to take it up again. Jesus was commanded by the Father to die for all men and the love of Jesus acquiesced to that plan. The effect of the love of the Father and the Son, both for each other and mankind, was sacrifice.
True love is proven, tried and strengthened by the readiness and capability to sacrifice.
God's love is rooted in sacrifice and He desires our love to be as strong and unfaltering as His. We must not only possess that love, but we must ever remain in that love. Our love for Him is proven by our fidelity in time of stress and pain. Love is not proven by feeling good, but by being good. Love is not made stronger in consolation, but in desolation.