Whatever you focus upon expands.  If you set your mind upon the external world, this will assume increasing importance in your life.  Spiritual growth will increasingly become a hobby or something to be crammed into your spare time.  If you vigorously dispute this, ask yourself the following questions:  Do you make sure you get three full meals a day? Do you also make sure that you pray and meditate three times a day for the same amount of time? Do you see the point and the problem? Whatever is most important to you is what you spend most of your time doing and thinking about. This is why most spiritual traditions advise against the external focus, which the pursuit of material wealth entails. The Spiritual Masters know human nature too well. They know that given half a chance, we will veer from the path and go off chasing soap bubbles.

Happily, there can be a satisfactory resolution to this. The answer is twofold. The first principle is that if you make your spiritual path your primary focus, then you will eventually master laws of the universe to ensure your abundance forever. Moreover, abundance here is interpreted in the widest possible way, including many ways that we cannot conceive of with finite minds! If you can truly tune yourself to the ultimate Source of all abundance in the universe, and that Source being God, then how can you remain poor in any sense? This is what Jesus had in mind when he said, "But seek ye first the kingdom of God and His righteousness: and all these things shall be added to you." (Matthew 6:33, NKJV)  In other words, bring your finite Mind and Being increasingly in tune with the Source of infinite abundance, and you cannot help but manifest abundance for yourself and others. This God given Source is "abundant life" and all about serving the self in others.  Knowing that all that you need, you already have within you. Moreover, you will do it with ease, at will, and to a greater level than you ever believed possible. If the universe is infinitely creative, then you are too, once you are in sync with the Holy Spirit.

The second principle - also implicit in the verse above - is to decide from the outset what your true life purpose and hence priority is. Then determine NEVER to let that balance between spiritual commitment and external effort be undermined. When we work upon an external goal - particularly financial abundance - it is VERY easy to allow that goal to consume an increasing amount of time and mental capacity.

Decide from the outset that you are going to focus upon the process of being excellent in the field of endeavor that is your life's purpose. Then pursue it with the intention of being the very best you can be, rather than focusing primarily upon some monetary result/goal at the end of the process. You can certainly have a monetary goal (chase the dream, your purpose, not the money).  However, beware of the danger of letting this become a primary obsession. Also, continually reassess the balance and level of commitment between your externally focused activities and your spiritual goals. Never let that balance slip.

In conclusion, it is possible to be financially abundant while following a spiritual path. However, it is very difficult - much more so than most personal development gurus would have you believe.  It is for this reason that the great Spiritual Masters strongly discouraged trying to do both.  Although, by using the two principles herein, it is possible to create abundance in your life in the widest possible sense of the word.