In Acts the early Church's organisation is described like this: 'All the believers were together and had everything in common. They sol property and possessions to give to anyone who had need'. Some view this view of community as communist in their approach.
Jesus taught in Matthew that 'you cannot serve both God and money'. If this is the case, then any sympathies with the Marxist approach could be argued to be coincidental.
Some natural theologians might argue that reason can be partially accurate outside the Church and so it is acceptable to be inspired by non-Christian approaches.
In the same way that Christians have successfully engaged with scientific developments, it is possible to remain Christian while embracing aspects of other ideologies.
The insights others can offer to the world can help Christians develop their responses. For example Freuds analysis of the mind might be helpful for Christians even if they do not completely accept his view.
Many secular ideologies may be atheist but do not directly contest religion.
If a valid atheist ideology successfully reverses the suffering of the oppressed then it should not just be ignored on the basis of faith. Orthopraxis is more important than orthodoxy.
Christians should not show sympathy for views that reject the existence of God.
Christians must remain distinctive and keep God and Jesus at the centre of their lives. There is enough in Jesus' teachings to guide life.
An atheist ideology such as Dawkins is too extreme in it's attack and might turn Christians from their faith.
The implications of atheist ideologies must always be acknowledged. Marxisms acceptance of violent revolution means that it should be rejected by Christianity.
If we are able to act in the moment as suggested by Bonhoeffer then we must clearly focus in our training on Christian beliefs.
It could be said that engage is a vague term. Christians should at the very least debate their ideas against secular ideologies which is a form of engagement.