وَقَالَ مُوسَىٰ يَٰقَوْمِ إِن كُنتُمْ ءَامَنتُم بِٱللَّهِ فَعَلَيْهِ تَوَكَّلُوٓا۟ إِن كُنتُم مُّسْلِمِينَ
Commentary:
The verse represents Moses as advising his people to realize that their work, viz. the work they were engaged in under his leadership, was God’s own work. This shows that Islam recognizes no narrow nationalism but requires its followers to work for God and His religion.
This is calculated to bring about a great change in a Muslim’s outlook on life. It helps him to think in terms of God, religion and righteousness and raises him above the narrow outlook of nationalism.
The words, if you indeed submit to His will, preceded by the expression, if you have believed in Allah, are not redundant but have been used to express an additional idea. When the word اسلام (submission) is used along with the word ایمان(belief), then the latter word signifies sincerity and firmness of faith while the former expresses only outward submission to authority. In other words, ایمان expresses "obedience of the heart," while اسلام signifies "outward or practical obedience." In this sense the verse would mean, "If you have acquired faith with regard to God and now you desire to taste the fruits thereof practically, then put your trust in God and entrust all your affairs to Him."
The verse thus teaches us that inner faith must be followed by a real outward change in the life of a person. For a true believer ایمان comes first and اسلام afterwards. But in the case of those weak of faith, اسلام takes precedence over ایمان because the weak of faith first begin with an outward expression of obedience and then gradually acquire heartfelt conviction. Thus in the case of a true believer purity of heart precedes purity of actions. But the reverse is the case of one who is weak of faith, for such a person stands in need of outside support for the purity of his heart. The purity of his actions, therefore, precedes the purity of his heart. It is to this fact that the Quran refers when it addresses the people of the desert in the words: Say, ye believe not, but rather say, We submit, for faith has not yet entered your hearts (49:15).
Iman signifies mental submission and Islam means outward obedience. Inner faith must be followed by real outward change in the conduct of a believer.