The Christo-trinitarian significance of this 'openness?'
The mysterious 'good' of the crucifixion, death and resurrection of Christ is that out of His 'opened' side comes the good of our redemption: the good of His bride, and our mother the Church: the good of His reconciliation of us to the Father and the 'sign' of this in the sending to us of the Holy Spirit: a good which at the same time 'testifies' to the mysterious openness which is fundamentally characteristic of the true person: the person who is at-one with God and man.
Thus, in order to be at-one with God and man one must be open to both God and man.
What, then, is the nature of this 'openness?'
This is perhaps one of the fundamental points in all this: there is a sense in which to live out of being open to God is to live out of the true uncertainty characteristic of a life lived in relation to the will of another: an uncertainty which arises - not out of instability, which it seems to resemble - but out of the nature of one person living out of their listening to another: a listening which is, in the reciprocal dialogue of relationships, a reciprocal act of each being open to the other (cf. Jn 14: 13-14 and 15: 16).
Nevertheless, it does not follow that there is no order of obedience to this relationship of reciprocal openness.
For instance, while Christ prayed to the Father to be spared the suffering of the crucifixion (Mt 26: 39), the Son submitted to what He understood to be the will of His Father to which He, as Son, was called to be obedient: a will of the Father which was to the Son as a drink (Mt 26: 42).
Thus, even though this involved no sin on the part of the Son, there is a sense of prayer turning the Son to the Father: almost as if the Son lives out of the will of the Father.
Finally, this sense of the obedience of one Person of the Blessed Trinity to another is further expressed in relation to the Holy Spirit: 'I will send him' the Counselor 'to you' (Jn 16: 7)., and 'he will not speak on his own authority, but whatever he hears he will speak' (Jn 16: 13); and it also entails the freedom of each one to give out of the other's fullness as the Blessed Trinity is, in some profoundly mysterious sense, an inherently reciprocally given Being67.
Christ says of all this: 'All that the Father has is mine; therefore I said that he 'the Counselor' will take what is mine and declare it to you' (Jn 16: 15).