Note 14 at Rom. 14:17: Man usually focuses his attention on external things such as meat and drink, but God is always concerned with the heart of man (1 Sam. 16:7). God deals with our actions because they indicate the condition of our hearts. But it is always the spiritual condition of our inner man that God is seeking to change.

Paul is saying that we need to be like God and focus on the inner condition of our brothers in Christ. Then we will be able to tolerate minor differences in their actions.