The easy use of physical means obscures the spiritual side of the question and is far from contributory to the awakening of individuals to their real dignity and freedom as spiritual beings. Thoughtless and uncontrolled indulgence must inevitably lead to reaction and spiritual bondage. For  spiritual aspirants in particular, but also for all human beings (because they are all potentially spiritual aspirants), it is extremely inadvisable to rely upon physical means for the regulation of childbearing. For such regulation the individuals must rely upon nothing but mental control.
Mental control secures the humanitarian purposes that inspire birth control but keeps clear of the spiritual disasters entailed by the use of physical means. Mental control is not only useful for regulating the number of children but is also indispensable for restoring to humanity its divine dignity and spiritual well-being. Only through the wise exercise of mental control is it possible for humanity to rise from passion to peace, from bondage to freedom, and from animality to purity. In the minds of thoughtful persons the much ignored spiritual side of this question must assume the importance it deserves.
– Discourses 7th Ed. p107
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“Mind is a good servant, but a bad master. This means if you control it, it will act as you want.”
(www.lordmeher.org, p2162)