The last few pages in ST I is full of quotable stuff. Tillich discusses the different symbols we use to describe God such as love, Father, Lord and it is brilliant stuff all the way. But I will leave that for you to look up on you own. Here's a quote on prayer, another example of how pious Tillich's theology is.
God's directing creativity is the answer to the question of the meaning of prayer, especially prayers of supplication and prayers of intercession. Neither type of prayer can mean that God is expected to acquiesce in interfering with existential conditions. Both mean that God is asked to direct the given situation toward fulfilment. The prayers are an element in this situation, a most powerful factor if they are true prayers. As an element in the situation a prayer is a condition of God's directing creativity, but the form of this creativity may be the complete rejection of the manifest content of the prayer. Nevertheless, the prayer may have been heard according to its hidden content which is the surrender of a fragment of existence to God. ... Every serious prayer contains power, not because of the intensity of desire expressed in it, but because of the faith the person has in God's directing activity - a faith which transforms the existential situation.
Systematic Theology I, 267.
You may want to read this quote a second time. Tillich's language is quite complex here. The context is a discussion on providence - God's directing creativity.
This quote includes in my opinion a very profound teaching on prayer, but I leave it to you to explore these concepts. Instead I'd like to share my opinion on how one should really read Tillich, and this quote is a great example of this. Tillich's goal is not to create a perfect philosophical system, or really to reinterpret the Christian tradition. The reason he creates this new language is to be able to say things like this, and remain honest. What Tillich does is essentially to create a language where there is room for the religious experience, since our everyday language no longer has that room. This is what Tillich means with apologetics - not to argue for the validity of Christianity with nifty philosophical arguments. That is also why his theology feels so important - it is built on a very honest understanding of the problem of religion in our time.