"Open up" versus "do what matters"? The impact of religion on psychological flexibility and depressive symptoms studied in the context of waiting list interventions with Christian clients.

Acceptance and Commitment Therapy (ACT) is an emerging treatment that focuses not so much on reducing or changing painful feelings or thoughts, but rather on learning to deal with painful feelings and thoughts, so that the patient can focus on what really important in his or her life. It is about acceptance and a commitment to a value-oriented life. (Hayes et al., 2012; Jansen & Batink, 2014). To achieve this, treatment is aimed to develop psychological flexibility, which consists of six interconnected core processes. These are acceptance, cognitive defusion, mindfullness, self as context, values and committed action. ACT is an effective treatment for various mental disorders, including depression. (Smout, 2012; Ruiz, 2010; Ruiz, 2012; Öst, 2014, A-Tjak, 2015; Hacker, 2016). Short-term ACT interventions are also effective in reducing depressive symptoms (Ruiz et al., 2018; Kroska, 2018; Kyllönen et al., 2018).Short-term ACT interventions can therefore contribute to making mental healthcare more efficient and also be used as a waiting list intervention, which is very relevant, given the current problems within the GGZ with regard to waiting lists and costs.,

Religion is an important part of a person's life and influences the level of psychological and physical well-being (Koenig et al., 2012). ) Many patients in the GGZ are religious and use religion as a coping mechanism for their psychological and physical complaints. It is therefore important to pay attention to religious factors in mental health care for these patients. (Weisman de Mamani, 2010, Hook, 2010). By focusing on accepting complaints and learning to live in a value-oriented way, ACT is close to the religious characteristics of many patients (Karekla & Constantinou, 2010). In the Christian faith the emphasis is also on accepting the suffering (Matthew 16:24) and living according to the values of your faith (Knabb, 2014). Various authors therefore argue that ACT can be well applied in the treatment of Christian religious patients and propose how ACT could be adapted for the treatment of this group of patients (Knabb, 2016; Rosales, 2016; Sisemore et al., 2014).

By implication, the goal of ACT for Christian patients seems to be to accept suffering in the here and now, to live by the beliefs religious values that God has for you. (Rosales, 2016, Knabb, 2014). However, this can lead to dilemmas in the treatment of Christian patients. For example, in the treatment of a depressed Christian religious woman with a bad marriage, is it important to accept her bad marriage and to focus treatment on accepting suffering, or is an open attitude to all the values that are important to her necessary, what is possible at the expense of her marriage? To see what influence religion can have on the effectiveness of ACT, it is relevant to see if there is a difference in effectiveness for religious patients between an ACT intervention focused on acceptance and an ACT intervention focused on values, with an open attitude to all values . The distribution made by Harris (2009) with regard to psychological flexibility is used for this. The accepting intervention will consist of interventions appropriate to acceptance and defusion and falls under what Harris calls "open up." The value-oriented intervention will consist of interventions appropriate to values and dedicated action and will fall under what Harris calls "do what matters."

The primary goal of this study is to understand how the Christian faith is associated with psychological flexibility and the effectiveness of specific ACT interventions. This makes a better assessment of choices in the ACT treatment of Christian patients with depressive symptoms possible. However, this research also links up with a growing line of research into the effectiveness of short-term ACT interventions in depressed patients. Given the shortages in mental health care, effective use of resources is important and it is therefore of great importance to gain more insight into the effectiveness of short-term interventions.

- The effectiveness of an ACT intervention focused on values and willingness to take action is more effective in reducing depressive symptoms two weeks after the intervention, compared to an an ACT intervention focused on acceptance and defusion and compared to a controlgroup without an intervention.
- The effectiveness of an ACT intervention focused on values and willingness to take action is more effective in reducing depressive symptoms twelve weeks after the intervention, compared to an an ACT intervention focused on acceptance and defusion and compared to a controlgroup without an intervention.
- An ACT intervention focused on values and willingness leads to a higher score on a measure of value-oriented life and not to a higher score on a measure of acceptance two weeks after the intervention.
- An ACT intervention focused on acceptance and defusion leads to a higher score on a measure of acceptance and not to a higher score on a measure of value-oriented life two weeks after the intervention.

There are two time points.

The intervention is a short-term, single-session ACT intervention during the waiting list period. There are three groups in the study:
1. Experimental condition A: Patients who receive a short-term single-session ACT intervention focused on values and willingness to take action.
2. Experimental condition B: Patients who receive a short-term single-session ACT intervention aimed at acceptance and defusion.
3. Control condition: Patients who are not offered an intervention.